Provided by: postfix_3.3.0-1ubuntu2_amd64 bug

NAME

       postconf - Postfix configuration parameters

SYNOPSIS

       postconf parameter ...

       postconf -e "parameter=value" ...

DESCRIPTION

       The  Postfix main.cf configuration file specifies parameters that control the operation of
       the Postfix mail  system.  Typically  the  file  contains  only  a  small  subset  of  all
       parameters; parameters not specified are left at their default values.

       The general format of the main.cf file is as follows:

       ·      Each  logical  line has the form "parameter = value".  Whitespace around the "=" is
              ignored, as is whitespace at the end of a logical line.

       ·      Empty lines and whitespace-only lines are ignored, as are lines  whose  first  non-
              whitespace character is a `#'.

       ·      A  logical line starts with non-whitespace text. A line that starts with whitespace
              continues a logical line.

       ·      A parameter value may refer to other parameters.

              ·      The expressions "$name" and "${name}"  are  recursively  replaced  with  the
                     value  of  the  named  parameter.  The  parameter  name  must  contain  only
                     characters from the  set  [a-zA-Z0-9_].  An  undefined  parameter  value  is
                     replaced with the empty value.

              ·      The  expressions  "${name?value}"  and  "${name?{value}}"  are replaced with
                     "value" when "$name" is non-empty. The  parameter  name  must  contain  only
                     characters from the set [a-zA-Z0-9_]. These forms are supported with Postfix
                     versions >= 2.2 and >= 3.0, respectively.

              ·      The expressions "${name:value}"  and  "${name:{value}}"  are  replaced  with
                     "value"  when  "$name"  is  empty.  The  parameter  name  must  contain only
                     characters from the set [a-zA-Z0-9_]. These forms are supported with Postfix
                     versions >= 2.2 and >= 3.0, respectively.

              ·      The  expression  "${name?{value1}:{value2}}"  is replaced with "value1" when
                     "$name" is non-empty, and with "value2" when "$name" is empty.  The "{}"  is
                     required  for  "value1",  optional  for  "value2".  The  parameter name must
                     contain only characters from the set [a-zA-Z0-9_].  This form  is  supported
                     with Postfix versions >= 3.0.

              ·      The  first  item inside "${...}" may be a relational expression of the form:
                     "{value3}  ==  {value4}".  Besides  the  "=="  (equality)  operator  Postfix
                     supports  "!="  (inequality),  "<",  "<=",  ">=", and ">". The comparison is
                     numerical when both operands are all digits,  otherwise  the  comparison  is
                     lexicographical. These forms are supported with Postfix versions >= 3.0.

              ·      Each  "value"  is  subject  to  recursive  named  parameter  and  relational
                     expression evaluation, except where noted.

              ·      Whitespace before or after each "{value}" is ignored.

              ·      Specify "$$" to produce a single "$" character.

              ·      The legacy form "$(...)" is equivalent to the preferred form "${...}".

       ·      When the same parameter is defined  multiple  times,  only  the  last  instance  is
              remembered.

       ·      Otherwise, the order of main.cf parameter definitions does not matter.

       The  remainder  of this document is a description of all Postfix configuration parameters.
       Default values are shown after the parameter name in parentheses, and  can  be  looked  up
       with the "postconf -d" command.

       Note:  this  is  not  an  invitation  to make changes to Postfix configuration parameters.
       Unnecessary changes can impair the operation of the mail system.

2bounce_notice_recipient (default: postmaster)

       The recipient of undeliverable mail that cannot be returned to the sender.   This  feature
       is enabled with the notify_classes parameter.

access_map_defer_code (default: 450)

       The  numerical  Postfix  SMTP  server  response  code for an access(5) map "defer" action,
       including "defer_if_permit" or "defer_if_reject". Prior to Postfix 2.6,  the  response  is
       hard-coded as "450".

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.6 and later.

access_map_reject_code (default: 554)

       The numerical Postfix SMTP server response code for an access(5) map "reject" action.

       Do not change this unless you have a complete understanding of RFC 5321.

address_verify_cache_cleanup_interval (default: 12h)

       The  amount  of  time  between  verify(8) address verification database cleanup runs. This
       feature requires that  the  database  supports  the  "delete"  and  "sequence"  operators.
       Specify a zero interval to disable database cleanup.

       After each database cleanup run, the verify(8) daemon logs the number of entries that were
       retained and dropped. A cleanup run is logged as  "partial"  when  the  daemon  terminates
       early after "postfix reload", "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.7.

address_verify_default_transport (default: $default_transport)

       Overrides the default_transport parameter setting for address verification probes.

       This feature is available in Postfix 2.1 and later.

address_verify_local_transport (default: $local_transport)

       Overrides the local_transport parameter setting for address verification probes.

       This feature is available in Postfix 2.1 and later.

address_verify_map (default: see postconf -d output)

       Lookup  table for persistent address verification status storage.  The table is maintained
       by the verify(8) service, and is opened before the process releases privileges.

       The lookup table is persistent by default (Postfix 2.7 and later).  Specify an empty table
       name  to  keep  the information in volatile memory which is lost after "postfix reload" or
       "postfix stop". This is the default with Postfix version 2.6 and earlier.

       Specify a location in a file system that  will  not  fill  up.  If  the  database  becomes
       corrupted,  the  world  comes to an end. To recover delete (NOT: truncate) the file and do
       "postfix reload".

       Postfix daemon processes do not use root privileges when opening this  file  (Postfix  2.5
       and later).  The file must therefore be stored under a Postfix-owned directory such as the
       data_directory.  As a migration aid, an attempt to  open  the  file  under  a  non-Postfix
       directory is redirected to the Postfix-owned data_directory, and a warning is logged.

       Examples:

       address_verify_map = hash:/var/lib/postfix/verify
       address_verify_map = btree:/var/lib/postfix/verify

       This feature is available in Postfix 2.1 and later.

address_verify_negative_cache (default: yes)

       Enable  caching  of  failed  address  verification  probe  results.   When this feature is
       enabled, the cache may pollute quickly with  garbage.   When  this  feature  is  disabled,
       Postfix will generate an address probe for every lookup.

       This feature is available in Postfix 2.1 and later.

address_verify_negative_expire_time (default: 3d)

       The time after which a failed probe expires from the address verification cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_negative_refresh_time (default: 3h)

       The time after which a failed address verification probe needs to be refreshed.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_pending_request_limit (default: see postconf -d output)

       A  safety  limit that prevents address verification requests from overwhelming the Postfix
       queue. By default, the number of pending requests is limited to 1/4 of  the  active  queue
       maximum  size  (qmgr_message_active_limit).  The  queue  manager  enforces  the  limit  by
       tempfailing requests that exceed the  limit.  This  affects  only  unknown  addresses  and
       inactive addresses that have expired, because the verify(8) daemon automatically refreshes
       an active address before it expires.

       This feature is available in Postfix 3.1 and later.

address_verify_poll_count (default: normal: 3, overload: 1)

       How many  times  to  query  the  verify(8)  service  for  the  completion  of  an  address
       verification request in progress.

       By  default,  the  Postfix SMTP server polls the verify(8) service up to three times under
       non-overload conditions, and only once when under overload.  With Postfix version 2.5  and
       earlier, the SMTP server always polls the verify(8) service up to three times by default.

       Specify  1  to  implement  a  crude  form  of greylisting, that is, always defer the first
       delivery request for a new address.

       Examples:

       # Postfix <= 2.6 default
       address_verify_poll_count = 3
       # Poor man's greylisting
       address_verify_poll_count = 1

       This feature is available in Postfix 2.1 and later.

address_verify_poll_delay (default: 3s)

       The delay between queries for  the  completion  of  an  address  verification  request  in
       progress.

       The default polling delay is 3 seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_expire_time (default: 31d)

       The time after which a successful probe expires from the address verification cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_refresh_time (default: 7d)

       The  time  after which a successful address verification probe needs to be refreshed.  The
       address verification status is not updated when the probe fails (optimistic caching).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_relay_transport (default: $relay_transport)

       Overrides the relay_transport parameter setting for address verification probes.

       This feature is available in Postfix 2.1 and later.

address_verify_relayhost (default: $relayhost)

       Overrides  the  relayhost  parameter  setting  for  address  verification   probes.   This
       information can be overruled with the transport(5) table.

       This feature is available in Postfix 2.1 and later.

address_verify_sender (default: $double_bounce_sender)

       The sender address to use in address verification probes; prior to Postfix 2.5 the default
       was "postmaster". To avoid problems with address probes  that  are  sent  in  response  to
       address  probes,  the Postfix SMTP server excludes the probe sender address from all SMTPD
       access blocks.

       Specify an empty value (address_verify_sender =) or <> if you want to use the null  sender
       address.  Beware,  some  sites  reject  mail  from  <>, even though RFCs require that such
       addresses be accepted.

       Examples:

       address_verify_sender = <>
       address_verify_sender = postmaster@my.domain

       This feature is available in Postfix 2.1 and later.

address_verify_sender_dependent_default_transport_maps (default:

       $sender_dependent_default_transport_maps)
       Overrides   the  sender_dependent_default_transport_maps  parameter  setting  for  address
       verification probes.

       This feature is available in Postfix 2.7 and later.

address_verify_sender_dependent_relayhost_maps (default: $sender_dependent_relayhost_maps)

       Overrides the sender_dependent_relayhost_maps parameter setting for  address  verification
       probes.

       This feature is available in Postfix 2.3 and later.

address_verify_sender_ttl (default: 0s)

       The  time  between  changes  in  the  time-dependent portion of address verification probe
       sender addresses. The time-dependent portion is appended to the localpart of  the  address
       specified with the address_verify_sender parameter. This feature is ignored when the probe
       sender addresses is the null sender, i.e. the address_verify_sender value is empty or <>.

       Historically, the probe sender address was fixed. This has caused such addresses to end up
       on spammer mailing lists, and has resulted in wasted network and processing resources.

       To  enable  time-dependent  probe  sender  addresses,  specify  a  non-zero time value (an
       integral value plus an optional one-letter suffix that specifies the time unit).   Specify
       a  value  of  at least several hours, to avoid problems with senders that use greylisting.
       Avoid nice TTL values, to make the result less predictable.  Time units are: s  (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.9 and later.

address_verify_service_name (default: verify)

       The  name of the verify(8) address verification service. This service maintains the status
       of sender and/or recipient address verification probes, and generates probes on request by
       other Postfix processes.

address_verify_transport_maps (default: $transport_maps)

       Overrides the transport_maps parameter setting for address verification probes.

       This feature is available in Postfix 2.1 and later.

address_verify_virtual_transport (default: $virtual_transport)

       Overrides the virtual_transport parameter setting for address verification probes.

       This feature is available in Postfix 2.1 and later.

alias_database (default: see postconf -d output)

       The  alias  databases  for  local(8)  delivery  that are updated with "newaliases" or with
       "sendmail -bi".

       This is a separate configuration parameter because  not  all  the  tables  specified  with
       $alias_maps have to be local files.

       Examples:

       alias_database = hash:/etc/aliases
       alias_database = hash:/etc/mail/aliases

alias_maps (default: see postconf -d output)

       The  alias  databases  that  are  used  for  local(8)  delivery. See aliases(5) for syntax
       details.  Specify zero or more "type:name"  lookup  tables,  separated  by  whitespace  or
       comma. Tables will be searched in the specified order until a match is found.  Note: these
       lookups are recursive.

       The default list is system dependent.  On systems with NIS, the default is to  search  the
       local alias database, then the NIS alias database.

       If  you  change  the alias database, run "postalias /etc/aliases" (or wherever your system
       stores the mail alias file), or simply run "newaliases" to build the necessary DBM  or  DB
       file.

       The  local(8)  delivery  agent  disallows  regular  expression  substitution of $1 etc. in
       alias_maps, because that would open a security hole.

       The local(8) delivery agent will silently ignore requests to use  the  proxymap(8)  server
       within  alias_maps.  Instead  it will open the table directly. Before Postfix version 2.2,
       the local(8) delivery agent will terminate with a fatal error.

       Examples:

       alias_maps = hash:/etc/aliases, nis:mail.aliases
       alias_maps = hash:/etc/aliases

allow_mail_to_commands (default: alias, forward)

       Restrict local(8) mail delivery to external commands.  The default is to disallow delivery
       to  "|command"  in  :include:   files  (see  aliases(5)  for  the  text  that defines this
       terminology).

       Specify zero or more of: alias,  forward  or  include,  in  order  to  allow  commands  in
       aliases(5), .forward files or in :include:  files, respectively.

       Example:

       allow_mail_to_commands = alias,forward,include

allow_mail_to_files (default: alias, forward)

       Restrict local(8) mail delivery to external files. The default is to disallow "/file/name"
       destinations  in  :include:   files  (see  aliases(5)  for  the  text  that  defines  this
       terminology).

       Specify  zero  or  more  of:  alias,  forward  or  include, in order to allow "/file/name"
       destinations in aliases(5), .forward files and in :include:  files, respectively.

       Example:

       allow_mail_to_files = alias,forward,include

allow_min_user (default: no)

       Allow a sender or recipient address to have `-' as the first character.  By default,  this
       is  not  allowed,  to  avoid  accidents  with software that passes email addresses via the
       command line. Such software would not be able to distinguish a malicious  address  from  a
       bona  fide  command-line option. Although this can be prevented by inserting a "--" option
       terminator into the command line, this is difficult to enforce consistently and globally.

       As of Postfix version 2.5,  this  feature  is  implemented  by  trivial-rewrite(8).   With
       earlier  versions  this  feature  was  implemented by qmgr(8) and was limited to recipient
       addresses only.

allow_percent_hack (default: yes)

       Enable the rewriting of the form "user%domain"  to  "user@domain".   This  is  enabled  by
       default.

       Note: as of Postfix version 2.2, message header address rewriting happens only when one of
       the following conditions is true:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The   message   is    received    from    a    network    client    that    matches
              $local_header_rewrite_clients,

       ·      The  message  is  received  from  the network, and the remote_header_rewrite_domain
              parameter specifies a non-empty value.

       To get the behavior before Postfix version 2.2,  specify  "local_header_rewrite_clients  =
       static:all".

       Example:

       allow_percent_hack = no

allow_untrusted_routing (default: no)

       Forward  mail  with  sender-specified  routing  (user[@%!]remote[@%!]site)  from untrusted
       clients to destinations matching $relay_domains.

       By default, this feature is turned off.  This closes a nasty open relay loophole  where  a
       backup  MX  host  can be tricked into forwarding junk mail to a primary MX host which then
       spams it out to the world.

       This parameter also controls if non-local  addresses  with  sender-specified  routing  can
       match  Postfix  access  tables.  By  default,  such  addresses cannot match Postfix access
       tables, because the address is ambiguous.

alternate_config_directories (default: empty)

       A list of non-default Postfix configuration directories that may  be  specified  with  "-c
       config_directory"  on the command line (in the case of sendmail(1), with the "-C" option),
       or via the MAIL_CONFIG environment parameter.

       This list must be specified in the default Postfix main.cf  file,  and  will  be  used  by
       set-gid Postfix commands such as postqueue(1) and postdrop(1).

       Specify  absolute  pathnames,  separated  by  comma or space. Note: $name expansion is not
       supported.

always_add_missing_headers (default: no)

       Always add (Resent-) From:, To:, Date: or Message-ID: headers when not  present.   Postfix
       2.6  and  later add these headers only when clients match the local_header_rewrite_clients
       parameter setting.  Earlier Postfix versions always add these headers; this may break DKIM
       signatures  that  cover non-existent headers.  The undisclosed_recipients_header parameter
       setting determines whether a To: header will be added.

always_bcc (default: empty)

       Optional address that receives a "blind carbon copy" of each message that is  received  by
       the Postfix mail system.

       Note:  with  Postfix  2.3  and  later the BCC address is added as if it was specified with
       NOTIFY=NONE. The sender will not be notified when the BCC  address  is  undeliverable,  as
       long as all down-stream software implements RFC 3461.

       Note:  with  Postfix  2.2  and earlier the sender will be notified when the BCC address is
       undeliverable.

       Note: automatic BCC recipients are produced only for new mail.   To  avoid  mailer  loops,
       automatic  BCC  recipients  are  not  generated after Postfix forwards mail internally, or
       after Postfix generates mail itself.

anvil_rate_time_unit (default: 60s)

       The time unit over which client connection rates and other rates are calculated.

       This feature is implemented by the anvil(8) service which is available in Postfix  version
       2.2 and later.

       The  default  interval  is relatively short. Because of the high frequency of updates, the
       anvil(8) server uses volatile memory only. Thus, information is lost whenever the  process
       terminates.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

anvil_status_update_time (default: 600s)

       How  frequently  the  anvil(8)  connection  and  rate  limiting  server  logs  peak  usage
       information.

       This feature is available in Postfix 2.2 and later.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

append_at_myorigin (default: yes)

       With locally submitted mail, append the string  "@$myorigin"  to  mail  addresses  without
       domain    information.    With    remotely    submitted    mail,    append    the   string
       "@$remote_header_rewrite_domain" instead.

       Note 1: this feature is enabled by default and must not be turned off.  Postfix  does  not
       support domain-less addresses.

       Note  2:  with Postfix version 2.2, message header address rewriting happens only when one
       of the following conditions is true:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The   message   is    received    from    a    network    client    that    matches
              $local_header_rewrite_clients,

       ·      The  message  is  received  from  the network, and the remote_header_rewrite_domain
              parameter specifies a non-empty value.

       To get the behavior before Postfix version 2.2,  specify  "local_header_rewrite_clients  =
       static:all".

append_dot_mydomain (default: Postfix >= 3.0: no, Postfix < 3.0: yes)

       With  locally  submitted  mail,  append  the string ".$mydomain" to addresses that have no
       ".domain"   information.   With   remotely   submitted    mail,    append    the    string
       ".$remote_header_rewrite_domain" instead.

       Note  1:  this  feature is enabled by default. If disabled, users will not be able to send
       mail to "user@partialdomainname" but will have to specify full domain names instead.

       Note 2: with Postfix version 2.2, message header address rewriting happens only  when  one
       of the following conditions is true:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The    message    is    received    from    a    network    client   that   matches
              $local_header_rewrite_clients,

       ·      The message is received from  the  network,  and  the  remote_header_rewrite_domain
              parameter specifies a non-empty value.

       To  get  the  behavior before Postfix version 2.2, specify "local_header_rewrite_clients =
       static:all".

application_event_drain_time (default: 100s)

       How long the postkick(1) command waits for a request to enter the Postfix  daemon  process
       input buffer before giving up.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

authorized_flush_users (default: static:anyone)

       List of users who are authorized to flush the queue.

       By default, all users are allowed to flush the queue.  Access is  always  granted  if  the
       invoking  user  is the super-user or the $mail_owner user.  Otherwise, the real UID of the
       process is looked up in the system password file,  and  access  is  granted  only  if  the
       corresponding  login  name  is  on  the  access  list.  The username "unknown" is used for
       processes whose real UID is not found in the password file.

       Specify a list of user names, "/file/name" or "type:table" patterns, separated  by  commas
       and/or  whitespace.  The  list is matched left to right, and the search stops on the first
       match. A "/file/name" pattern is replaced by its contents; a "type:table" lookup table  is
       matched  when  a  name matches a lookup key (the lookup result is ignored).  Continue long
       lines by starting the next line with whitespace. Specify "!pattern" to exclude a name from
       the list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_mailq_users (default: static:anyone)

       List of users who are authorized to view the queue.

       By  default,  all  users  are  allowed to view the queue.  Access is always granted if the
       invoking user is the super-user or the $mail_owner user.  Otherwise, the real UID  of  the
       process  is  looked  up  in  the  system  password file, and access is granted only if the
       corresponding login name is on the access  list.   The  username  "unknown"  is  used  for
       processes whose real UID is not found in the password file.

       Specify  a  list of user names, "/file/name" or "type:table" patterns, separated by commas
       and/or whitespace. The list is matched left to right, and the search stops  on  the  first
       match.  A "/file/name" pattern is replaced by its contents; a "type:table" lookup table is
       matched when a name matches a lookup key (the lookup result is  ignored).   Continue  long
       lines by starting the next line with whitespace. Specify "!pattern" to exclude a user name
       from the list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_submit_users (default: static:anyone)

       List of users who are authorized to submit mail with the sendmail(1) command (and with the
       privileged postdrop(1) helper command).

       By  default, all users are allowed to submit mail.  Otherwise, the real UID of the process
       is looked up in the system password file, and access is granted only if the  corresponding
       login name is on the access list.  The username "unknown" is used for processes whose real
       UID is not found in the password file. To deny mail submission access to all users specify
       an empty list.

       Specify  a  list of user names, "/file/name" or "type:table" patterns, separated by commas
       and/or whitespace. The list is matched left to right, and the search stops  on  the  first
       match.  A "/file/name" pattern is replaced by its contents; a "type:table" lookup table is
       matched when a name matches a lookup key (the lookup result is  ignored).   Continue  long
       lines by starting the next line with whitespace. Specify "!pattern" to exclude a user name
       from the list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

       Example:

       authorized_submit_users = !www, static:all

       This feature is available in Postfix 2.2 and later.

authorized_verp_clients (default: $mynetworks)

       What remote SMTP clients are allowed to specify the XVERP command.  This command  requests
       that mail be delivered one recipient at a time with a per recipient return address.

       By default, only trusted clients are allowed to specify XVERP.

       This  parameter was introduced with Postfix version 1.1.  Postfix version 2.1 renamed this
       parameter to smtpd_authorized_verp_clients and changed the default to none.

       Specify a list of network/netmask patterns, separated by  commas  and/or  whitespace.  The
       mask  specifies  the  number  of  bits in the network part of a host address. You can also
       specify hostnames or .domain names (the initial dot causes the domain to  match  any  name
       below  it),  "/file/name" or "type:table" patterns.  A "/file/name" pattern is replaced by
       its contents; a "type:table" lookup table is matched when a table entry matches  a  lookup
       string (the lookup result is ignored).  Continue long lines by starting the next line with
       whitespace. Specify "!pattern" to exclude an address or network block from the  list.  The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note:   IP   version   6   address   information  must  be  specified  inside  []  in  the
       authorized_verp_clients value, and in files specified with  "/file/name".   IP  version  6
       addresses  contain  the ":" character, and would otherwise be confused with a "type:table"
       pattern.

backwards_bounce_logfile_compatibility (default: yes)

       Produce additional bounce(8) logfile records that can be read by Postfix  versions  before
       2.0. The current and more extensible "name = value" format is needed in order to implement
       more sophisticated functionality.

       This feature is available in Postfix 2.1 and later.

berkeley_db_create_buffer_size (default: 16777216)

       The per-table I/O buffer size for programs that create Berkeley DB hash or  btree  tables.
       Specify a byte count.

       This feature is available in Postfix 2.0 and later.

berkeley_db_read_buffer_size (default: 131072)

       The  per-table  I/O  buffer  size for programs that read Berkeley DB hash or btree tables.
       Specify a byte count.

       This feature is available in Postfix 2.0 and later.

best_mx_transport (default: empty)

       Where the Postfix SMTP client should deliver mail when it detects a "mail  loops  back  to
       myself"  error  condition. This happens when the local MTA is the best SMTP mail exchanger
       for a destination  not  listed  in  $mydestination,  $inet_interfaces,  $proxy_interfaces,
       $virtual_alias_domains,  or $virtual_mailbox_domains.  By default, the Postfix SMTP client
       returns such mail as undeliverable.

       Specify, for example, "best_mx_transport = local" to pass the mail from the  Postfix  SMTP
       client to the local(8) delivery agent. You can specify any message delivery "transport" or
       "transport:nexthop" that is defined in the master.cf file.  See  the  transport(5)  manual
       page for the syntax and meaning of "transport" or "transport:nexthop".

       However,  this feature is expensive because it ties up a Postfix SMTP client process while
       the local(8) delivery agent is doing its work. It is more efficient (for Postfix) to  list
       all hosted domains in a table or database.

biff (default: yes)

       Whether or not to use the local biff service.  This service sends "new mail" notifications
       to users who have requested new mail notification with the UNIX command "biff y".

       For compatibility reasons this feature  is  on  by  default.   On  systems  with  lots  of
       interactive  users,  the  biff service can be a performance drain.  Specify "biff = no" in
       main.cf to disable.

body_checks (default: empty)

       Optional lookup tables for content inspection as specified in  the  body_checks(5)  manual
       page.

       Note:  with Postfix versions before 2.0, these rules inspect all content after the primary
       message headers.

body_checks_size_limit (default: 51200)

       How much text in a message body segment (or attachment, if you prefer to use that term) is
       subjected to body_checks inspection.  The amount of text is limited to avoid scanning huge
       attachments.

       This feature is available in Postfix 2.0 and later.

bounce_notice_recipient (default: postmaster)

       The recipient of postmaster notifications with the message headers of  mail  that  Postfix
       did not deliver and of SMTP conversation transcripts of mail that Postfix did not receive.
       This feature is enabled with the notify_classes parameter.

bounce_queue_lifetime (default: 5d)

       Consider a bounce message as undeliverable, when delivery fails with  a  temporary  error,
       and  the  time in the queue has reached the bounce_queue_lifetime limit.  By default, this
       limit is the same as for regular mail.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is d (days).

       Specify 0 when mail delivery should be tried only once.

       This feature is available in Postfix 2.1 and later.

bounce_service_name (default: bounce)

       The  name  of  the  bounce(8)  service. This service maintains a record of failed delivery
       attempts and generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

bounce_size_limit (default: 50000)

       The maximal amount of original message text that is sent in a  non-delivery  notification.
       Specify  a  byte  count.   A  message  is  returned as either message/rfc822 (the complete
       original) or as text/rfc822-headers (the headers only).   With  Postfix  version  2.4  and
       earlier,  a  message is always returned as message/rfc822 and is truncated when it exceeds
       the size limit.

       Notes:

       ·      If you increase this limit, then you should increase the  mime_nesting_limit  value
              proportionally.

       ·      Be  careful  when making changes.  Excessively large values will result in the loss
              of non-delivery notifications, when a bounce message size exceeds a local or remote
              MTA's message size limit.

bounce_template_file (default: empty)

       Pathname  of  a  configuration  file  with  bounce  message templates.  These override the
       built-in templates of delivery status notification (DSN) messages for undeliverable  mail,
       for delayed mail, successful delivery, or delivery verification. The bounce(5) manual page
       describes how to edit and test template files.

       Template  message  body  text  may  contain  $name  references  to  Postfix  configuration
       parameters.  The  result  of $name expansion can be previewed with "postconf -b file_name"
       before the file is placed into the Postfix configuration directory.

       This feature is available in Postfix 2.3 and later.

broken_sasl_auth_clients (default: no)

       Enable interoperability with remote SMTP clients that implement an obsolete version of the
       AUTH  command (RFC 4954). Examples of such clients are MicroSoft Outlook Express version 4
       and MicroSoft Exchange version 5.0.

       Specify "broken_sasl_auth_clients = yes" to have  Postfix  advertise  AUTH  support  in  a
       non-standard way.

canonical_classes (default: envelope_sender, envelope_recipient, header_sender, header_recipient)


       What addresses are subject to canonical_maps address mapping.  By default,  canonical_maps
       address  mapping  is  applied  to  envelope  sender and recipient addresses, and to header
       sender and header recipient addresses.

       Specify   one   or   more   of:   envelope_sender,   envelope_recipient,    header_sender,
       header_recipient

       This feature is available in Postfix 2.2 and later.

canonical_maps (default: empty)

       Optional  address  mapping lookup tables for message headers and envelopes. The mapping is
       applied to both sender and recipient addresses, in  both  envelopes  and  in  headers,  as
       controlled  with the canonical_classes parameter. This is typically used to clean up dirty
       addresses from legacy mail systems, or to replace login names by Firstname.Lastname.   The
       table  format  and  lookups  are  documented  in  canonical(5). For an overview of Postfix
       address manipulations see the ADDRESS_REWRITING_README document.

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.  Tables
       will  be  searched in the specified order until a match is found.  Note: these lookups are
       recursive.

       If you use this feature, run "postmap /etc/postfix/canonical" to build the  necessary  DBM
       or  DB file after every change. The changes will become visible after a minute or so.  Use
       "postfix reload" to eliminate the delay.

       Note: with Postfix version 2.2, message header address mapping happens only  when  message
       header address rewriting is enabled:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The    message    is    received    from    a    network    client   that   matches
              $local_header_rewrite_clients,

       ·      The message is received from  the  network,  and  the  remote_header_rewrite_domain
              parameter specifies a non-empty value.

       To  get  the  behavior before Postfix version 2.2, specify "local_header_rewrite_clients =
       static:all".

       Examples:

       canonical_maps = dbm:/etc/postfix/canonical
       canonical_maps = hash:/etc/postfix/canonical

cleanup_service_name (default: cleanup)

       The name of the cleanup(8) service. This service  rewrites  addresses  into  the  standard
       form, and performs canonical(5) address mapping and virtual(5) aliasing.

       This feature is available in Postfix 2.0 and later.

command_directory (default: see postconf -d output)

       The location of all postfix administrative commands.

command_execution_directory (default: empty)

       The  local(8)  delivery agent working directory for delivery to external command.  Failure
       to change directory causes the delivery to be deferred.

       The  following  $name  expansions  are  done  on  command_execution_directory  before  the
       directory  is  changed.  Expansion  happens  in  the context of the delivery request.  The
       result of $name expansion is filtered with the character set that is  specified  with  the
       execution_directory_expansion_filter parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
              The full recipient address.

       $extension
              The optional recipient address extension.

       $domain
              The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
              The  address  extension  delimiter that was found in the recipient address (Postfix
              2.11 and later), or the system-wide recipient address extension delimiter  (Postfix
              2.10 and earlier).

       ${name?value}
              Expands to value when $name is non-empty.

       ${name:value}
              Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       This feature is available in Postfix 2.2 and later.

command_expansion_filter (default: see postconf -d output)

       Restrict  the  characters  that  the local(8) delivery agent allows in $name expansions of
       $mailbox_command and $command_execution_directory.  Characters outside the allowed set are
       replaced by underscores.

command_time_limit (default: 1000s)

       Time  limit for delivery to external commands. This limit is used by the local(8) delivery
       agent, and is the default time limit for delivery by the pipe(8) delivery agent.

       Note: if you set this time limit to a large value you must update the  global  ipc_timeout
       parameter as well.

compatibility_level (default: 0)

       A  safety  net that causes Postfix to run with backwards-compatible default settings after
       an upgrade to a newer Postfix version.

       With backwards compatibility turned on (the main.cf compatibility_level value is less than
       the  Postfix  built-in  value), Postfix looks for settings that are left at their implicit
       default value, and logs a message when a backwards-compatible default setting is required.

           using backwards-compatible default setting name=value
               to [accept a specific client request]

           using backwards-compatible default setting name=value
               to [enable specific Postfix behavior]

       See COMPATIBILITY_README for specific message details. If such a message is logged in  the
       context   of   a   legitimate   request,   the   system   administrator  should  make  the
       backwards-compatible setting permanent in main.cf or master.cf, for example:

           # postconf name=value
           # postfix reload

       When no more backwards-compatible settings need to be made  permanent,  the  administrator
       should  turn  off  backwards  compatibility by updating the compatibility_level setting in
       main.cf:

           # postconf compatibility_level=N
           # postfix reload

       For N specify the number that is logged in your postfix(1) warning message:

           warning: To disable backwards compatibility use "postconf
               compatibility_level=N" and "postfix reload"

       This feature is available in Postfix 3.0 and later.

config_directory (default: see postconf -d output)

       The default location of the Postfix main.cf and master.cf configuration files. This can be
       overruled via the following mechanisms:

       ·      The MAIL_CONFIG environment variable (daemon processes and commands).

       ·      The "-c" command-line option (commands only).

       With  Postfix  command  that  run  with  set-gid  privileges,  a config_directory override
       requires either root privileges, or it requires that the  directory  is  listed  with  the
       alternate_config_directories parameter in the default main.cf file.

confirm_delay_cleared (default: no)

       After  sending  a "your message is delayed" notification, inform the sender when the delay
       clears up. This can result in a sudden burst of notifications at the end  of  a  prolonged
       network outage, and is therefore disabled by default.

       See also: delay_warning_time.

       This feature is available in Postfix 3.0 and later.

connection_cache_protocol_timeout (default: 5s)

       Time  limit  for  connection cache connect, send or receive operations.  The time limit is
       enforced in the client.

       This feature is available in Postfix 2.3 and later.

connection_cache_service_name (default: scache)

       The name of the scache(8) connection cache service.  This service maintains a limited pool
       of cached sessions.

       This feature is available in Postfix 2.2 and later.

connection_cache_status_update_time (default: 600s)

       How  frequently  the  scache(8) server logs usage statistics with connection cache hit and
       miss rates for logical destinations and for physical endpoints.

connection_cache_ttl_limit (default: 2s)

       The maximal time-to-live value that the scache(8) connection cache server allows. Requests
       that specify a larger TTL will be stored with the maximum allowed TTL. The purpose of this
       additional control is to protect the infrastructure against careless people. The cache TTL
       is already bounded by $max_idle.

content_filter (default: empty)

       After   the   message   is   queued,   send   the   entire   message   to   the  specified
       transport:destination. The transport name specifies the first field  of  a  mail  delivery
       agent  definition in master.cf; the syntax of the next-hop destination is described in the
       manual page of the corresponding delivery agent.  More information about external  content
       filters is in the Postfix FILTER_README file.

       Notes:

       ·      This  setting  has  lower  precedence  than a FILTER action that is specified in an
              access(5), header_checks(5) or body_checks(5) table.

       ·      The meaning of an empty next-hop filter destination is version dependent.   Postfix
              2.7 and later will use the recipient domain; earlier versions will use $myhostname.
              Specify "default_filter_nexthop = $myhostname" for compatibility with  Postfix  2.6
              or   earlier,   or  specify  a  content_filter  value  with  an  explicit  next-hop
              destination.

cyrus_sasl_config_path (default: empty)

       Search path for Cyrus SASL application configuration files, currently used only to  locate
       the  $smtpd_sasl_path.conf  file.   Specify  zero or more directories separated by a colon
       character, or an empty value to use Cyrus SASL's built-in search path.

       This feature is available in Postfix 2.5 and later when compiled with Cyrus SASL 2.1.22 or
       later.

daemon_directory (default: see postconf -d output)

       The  directory  with  Postfix  support  programs and daemon programs.  These should not be
       invoked directly by humans. The directory must be owned by root.

daemon_table_open_error_is_fatal (default: no)

       How a  Postfix  daemon  process  handles  errors  while  opening  lookup  tables:  gradual
       degradation or immediate termination.

        no  (default)
              Gradual  degradation: a daemon process logs a message of type "error" and continues
              execution  with  reduced  functionality.  Features  that  do  not  depend  on   the
              unavailable  table will work normally, while features that depend on the table will
              result in a type "warning" message.
              When the notify_classes parameter value contains the "data" class, the Postfix SMTP
              server and client will report transcripts of sessions with an error because a table
              is unavailable.

        yes  (historical behavior)
              Immediate termination: a daemon process logs a type "fatal" message and  terminates
              immediately.   This  option  reduces  the  number  of  possible  code paths through
              Postfix, and may therefore be slightly more secure than the default.

       For the sake of sanity, the number of type "error" messages is  limited  to  13  over  the
       lifetime of a daemon process.

       This feature is available in Postfix 2.9 and later.

daemon_timeout (default: 18000s)

       How  much  time  a  Postfix  daemon  process  may  take  to  handle a request before it is
       terminated by a built-in watchdog timer.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

data_directory (default: see postconf -d output)

       The  directory  with  Postfix-writable  data  files  (for  example:  caches, pseudo-random
       numbers).  This directory must be owned by the mail_owner account, and must not be  shared
       with non-Postfix software.

       This feature is available in Postfix 2.5 and later.

debug_peer_level (default: 2)

       The increment in verbose logging level when a remote client or server matches a pattern in
       the debug_peer_list parameter.

debug_peer_list (default: empty)

       Optional list of remote client or server hostname or network address patterns  that  cause
       the verbose logging level to increase by the amount specified in $debug_peer_level.

       Specify  domain  names,  network/netmask  patterns,  "/file/name" patterns or "type:table"
       lookup tables. The right-hand side result from "type:table" lookups is ignored.

       Pattern  matching  of  domain  names  is  controlled  by  the  presence  or   absence   of
       "debug_peer_list" in the parent_domain_matches_subdomains parameter value.

       Examples:

       debug_peer_list = 127.0.0.1
       debug_peer_list = example.com

debugger_command (default: empty)

       The  external  command  to  execute  when  a Postfix daemon program is invoked with the -D
       option.

       Use "command .. & sleep 5" so that the debugger can attach before the process marches  on.
       If  you  use  an  X-based debugger, be sure to set up your XAUTHORITY environment variable
       before starting Postfix.

       Note: the command is subject to $name expansion,  before  it  is  passed  to  the  default
       command interpreter. Specify "$$" to produce a single "$" character.

       Example:

       debugger_command =
           PATH=/usr/bin:/usr/X11R6/bin
           ddd $daemon_directory/$process_name $process_id & sleep 5

default_database_type (default: see postconf -d output)

       The  default database type for use in newaliases(1), postalias(1) and postmap(1) commands.
       On many UNIX systems the default type is either dbm or hash. The default setting is frozen
       when the Postfix system is built.

       Examples:

       default_database_type = hash
       default_database_type = dbm

default_delivery_slot_cost (default: 5)

       How  often  the  Postfix  queue  manager's scheduler is allowed to preempt delivery of one
       message with another.

       Each transport maintains a so-called "available delivery slot counter" for  each  message.
       One  message can be preempted by another one when the other message can be delivered using
       no more delivery slots (i.e., invocations of delivery agents)  than  the  current  message
       counter has accumulated (or will eventually accumulate - see about slot loans below). This
       parameter controls  how  often  is  the  counter  incremented  -  it  happens  after  each
       default_delivery_slot_cost recipients have been delivered.

       The  cost of 0 is used to disable the preempting scheduling completely.  The minimum value
       the scheduling algorithm can use is 2 - use  it  if  you  want  to  maximize  the  message
       throughput  rate.  Although  there is no maximum, it doesn't make much sense to use values
       above say 50.

       The only reason why the value of 2 is not the default is the way  this  parameter  affects
       the  delivery  of  mailing-list mail. In the worst case, their delivery can take somewhere
       between (cost+1/cost) and (cost/cost-1) times more than if the  preemptive  scheduler  was
       disabled.  The  default  value of 5 turns out to provide reasonable message response times
       while making sure the mailing-list deliveries are not extended by more than 20-25  percent
       even in the worst case.

       Use transport_delivery_slot_cost to specify a transport-specific override, where transport
       is the master.cf name of the message delivery transport.

       Examples:

       default_delivery_slot_cost = 0
       default_delivery_slot_cost = 2

default_delivery_slot_discount (default: 50)

       The default value for transport-specific _delivery_slot_discount settings.

       This parameter speeds up the moment when a  message  preemption  can  happen.  Instead  of
       waiting  until the full amount of delivery slots required is available, the preemption can
       happen  when  transport_delivery_slot_discount  percent  of  the  required   amount   plus
       transport_delivery_slot_loan  still  remains to be accumulated.  Note that the full amount
       will still have to be accumulated before another preemption can take place later.

       Use transport_delivery_slot_discount  to  specify  a  transport-specific  override,  where
       transport is the master.cf name of the message delivery transport.

default_delivery_slot_loan (default: 3)

       The default value for transport-specific _delivery_slot_loan settings.

       This  parameter  speeds  up  the  moment  when a message preemption can happen. Instead of
       waiting until the full amount of delivery slots required is available, the preemption  can
       happen   when   transport_delivery_slot_discount  percent  of  the  required  amount  plus
       transport_delivery_slot_loan still remains to be accumulated.  Note that the  full  amount
       will still have to be accumulated before another preemption can take place later.

       Use transport_delivery_slot_loan to specify a transport-specific override, where transport
       is the master.cf name of the message delivery transport.

default_delivery_status_filter (default: empty)

       Optional filter to replace the delivery status code or explanatory text of  successful  or
       unsuccessful  deliveries.  This does not allow the replacement of a successful status code
       (2.X.X) with an unsuccessful status code (4.X.X or 5.X.X) or vice versa.

       Note: the (smtp|lmtp)_delivery_status_filter is applied  only  once  per  recipient:  when
       delivery  is  successful,  when  delivery  is rejected with 5XX, or when there are no more
       alternate MX or A destinations. Use  smtp_reply_filter  or  lmtp_reply_filter  to  inspect
       responses for all delivery attempts.

       The  following  parameters can be used to implement a filter for specific delivery agents:
       lmtp_delivery_status_filter,  local_delivery_status_filter,   pipe_delivery_status_filter,
       smtp_delivery_status_filter  or  virtual_delivery_status_filter.  These parameters support
       the same filter syntax as described here.

       Specify zero or more "type:table" lookup table names, separated by  comma  or  whitespace.
       For each successful or unsuccessful delivery to a recipient, the tables are queried in the
       specified order with one line of text that is structured as follows:

           enhanced-status-code SPACE explanatory-text

       The first table match wins. The lookup result must have the same structure as the query, a
       successful  status  code  (2.X.X)  must  be  replaced  with  a  successful status code, an
       unsuccessful status code (4.X.X or 5.X.X) must be replaced  with  an  unsuccessful  status
       code,  and  the  explanatory  text field must be non-empty. Other results will result in a
       warning.

       Example 1: convert specific soft TLS errors into hard  errors,  by  overriding  the  first
       number in the enhanced status code.

           /etc/postfix/main.cf:
               smtp_delivery_status_filter = pcre:/etc/postfix/smtp_dsn_filter

           /etc/postfix/smtp_dsn_filter:
               /^4(\.\d+\.\d+ TLS is required, but host \S+ refused to start TLS: .+)/
                   5$1
               /^4(\.\d+\.\d+ TLS is required, but was not offered by host .+)/
                   5$1
               # Do not change the following into hard bounces. They may
               # result from a local configuration problem.
               # 4.\d+.\d+ TLS is required, but our TLS engine is unavailable
               # 4.\d+.\d+ TLS is required, but unavailable
               # 4.\d+.\d+ Cannot start TLS: handshake failure

       Example  2:  censor  the per-recipient delivery status text so that it does not reveal the
       destination command or filename when a remote sender requests confirmation  of  successful
       delivery.

           /etc/postfix/main.cf:
               local_delivery_status_filter = pcre:/etc/postfix/local_dsn_filter

           /etc/postfix/local_dsn_filter:
               /^(2\S+ delivered to file).+/    $1
               /^(2\S+ delivered to command).+/ $1

       Notes:

       ·      This feature will NOT override the soft_bounce safety net.

       ·      This  feature  will  change the enhanced status code and text that is logged to the
              maillog file, and that is reported  to  the  sender  in  delivery  confirmation  or
              non-delivery notifications.

       This feature is available in Postfix 3.0 and later.

default_destination_concurrency_failed_cohort_limit (default: 1)

       How  many  pseudo-cohorts  must  suffer  connection or handshake failure before a specific
       destination is considered unavailable (and further delivery is suspended). Specify zero to
       disable  this  feature.  A  destination's pseudo-cohort failure count is reset each time a
       delivery completes without connection or handshake failure for that specific destination.

       A pseudo-cohort is the number of deliveries equal to a destination's delivery concurrency.

       Use transport_destination_concurrency_failed_cohort_limit to specify a  transport-specific
       override, where transport is the master.cf name of the message delivery transport.

       This  feature  is available in Postfix 2.5. The default setting is compatible with earlier
       Postfix versions.

default_destination_concurrency_limit (default: 20)

       The default maximal number of parallel deliveries to the same destination.   This  is  the
       default  limit  for  delivery  via  the  lmtp(8), pipe(8), smtp(8) and virtual(8) delivery
       agents.  With per-destination recipient limit > 1, a destination is a domain, otherwise it
       is a recipient.

       Use  transport_destination_concurrency_limit  to  specify  a  transport-specific override,
       where transport is the master.cf name of the message delivery transport.

default_destination_concurrency_negative_feedback (default: 1)

       The per-destination amount of delivery concurrency negative  feedback,  after  a  delivery
       completes  with  a  connection or handshake failure. Feedback values are in the range 0..1
       inclusive. With negative feedback, concurrency  is  decremented  at  the  beginning  of  a
       sequence  of  length  1/feedback.  This  is unlike positive feedback, where concurrency is
       incremented at the end of a sequence of length 1/feedback.

       As of Postfix version 2.5, negative feedback cannot reduce delivery concurrency  to  zero.
       Instead,  a  destination  is  marked  dead  (further  delivery suspended) after the failed
       pseudo-cohort  count  reaches   $default_destination_concurrency_failed_cohort_limit   (or
       $transport_destination_concurrency_failed_cohort_limit).  To make the scheduler completely
       immune to connection or handshake failures, specify a  zero  feedback  value  and  a  zero
       failed pseudo-cohort limit.

       Specify one of the following forms:

       number

       number / number
              Constant  feedback.  The  value  must  be in the range 0..1 inclusive.  The default
              setting  of  "1"  is  compatible  with  Postfix  versions  before  2.5,   where   a
              destination's  delivery concurrency is throttled down to zero (and further delivery
              suspended) after a single failed pseudo-cohort.

       number / concurrency
              Variable feedback of "number / (delivery concurrency)".  The number must be in  the
              range   0..1  inclusive.  With  number  equal  to  "1",  a  destination's  delivery
              concurrency is decremented by 1 after each failed pseudo-cohort.

       A pseudo-cohort is the number of deliveries equal to a destination's delivery concurrency.

       Use transport_destination_concurrency_negative_feedback to  specify  a  transport-specific
       override, where transport is the master.cf name of the message delivery transport.

       This  feature  is available in Postfix 2.5. The default setting is compatible with earlier
       Postfix versions.

default_destination_concurrency_positive_feedback (default: 1)

       The per-destination amount of delivery concurrency positive  feedback,  after  a  delivery
       completes  without  connection or handshake failure. Feedback values are in the range 0..1
       inclusive.  The  concurrency  increases  until  it  reaches  the  per-destination  maximal
       concurrency  limit.  With  positive  feedback,  concurrency is incremented at the end of a
       sequence with length 1/feedback. This is unlike negative feedback,  where  concurrency  is
       decremented at the start of a sequence of length 1/feedback.

       Specify one of the following forms:

       number

       number / number
              Constant  feedback.   The  value  must  be in the range 0..1 inclusive. The default
              setting  of  "1"  is  compatible  with  Postfix  versions  before  2.5,   where   a
              destination's delivery concurrency doubles after each successful pseudo-cohort.

       number / concurrency
              Variable  feedback of "number / (delivery concurrency)".  The number must be in the
              range  0..1  inclusive.  With  number  equal  to  "1",  a  destination's   delivery
              concurrency is incremented by 1 after each successful pseudo-cohort.

       A pseudo-cohort is the number of deliveries equal to a destination's delivery concurrency.

       Use  transport_destination_concurrency_positive_feedback  to  specify a transport-specific
       override, where transport is the master.cf name of the message delivery transport.

       This feature is available in Postfix 2.5 and later.

default_destination_rate_delay (default: 0s)

       The default amount of delay that is inserted between individual  deliveries  to  the  same
       destination;   the   resulting   behavior  depends  on  the  value  of  the  corresponding
       per-destination recipient limit.

       ·      With a corresponding per-destination recipient limit > 1, the rate delay  specifies
              the time between deliveries to the same domain.  Different domains are delivered in
              parallel, subject to the process limits specified in master.cf.

       ·      With a corresponding per-destination recipient limit equal to  1,  the  rate  delay
              specifies  the  time between deliveries to the same recipient. Different recipients
              are delivered in parallel, subject to the process limits specified in master.cf.

       To enable the delay, specify a non-zero time value (an integral  value  plus  an  optional
       one-letter suffix that specifies the time unit).

       Time  units:  s  (seconds),  m (minutes), h (hours), d (days), w (weeks). The default time
       unit is s (seconds).

       NOTE: the delay is enforced by the queue manager. The delay timer state does  not  survive
       "postfix reload" or "postfix stop".

       Use  transport_destination_rate_delay  to  specify  a  transport-specific  override, where
       transport is the master.cf name of the message delivery transport.

       NOTE:      with      a       non-zero       _destination_rate_delay,       specify       a
       transport_destination_concurrency_failed_cohort_limit  of  10  or  more to prevent Postfix
       from deferring all mail for the same destination after only one  connection  or  handshake
       error.

       This feature is available in Postfix 2.5 and later.

default_destination_recipient_limit (default: 50)

       The  default maximal number of recipients per message delivery.  This is the default limit
       for delivery via the lmtp(8), pipe(8), smtp(8) and virtual(8) delivery agents.

       Setting this parameter to a value of 1 affects email deliveries as follows:

       ·      It changes the meaning of the corresponding per-destination concurrency limit, from
              concurrency  of deliveries to the same domain into concurrency of deliveries to the
              same recipient.  Different recipients are delivered in  parallel,  subject  to  the
              process limits specified in master.cf.

       ·      It  changes  the  meaning of the corresponding per-destination rate delay, from the
              delay between deliveries to the same domain into the delay  between  deliveries  to
              the same recipient.  Again, different recipients are delivered in parallel, subject
              to the process limits specified in master.cf.

       ·      It changes the meaning of other corresponding per-destination settings in a similar
              manner, from settings for delivery to the same domain into settings for delivery to
              the same recipient.

       Use transport_destination_recipient_limit to specify a transport-specific override,  where
       transport is the master.cf name of the message delivery transport.

default_extra_recipient_limit (default: 1000)

       The  default  value  for  the extra per-transport limit imposed on the number of in-memory
       recipients.  This extra recipient space is reserved for the cases when the  Postfix  queue
       manager's  scheduler  preempts  one  message  with  another  and suddenly needs some extra
       recipients slots for the chosen message in order to avoid performance degradation.

       Use  transport_extra_recipient_limit  to  specify  a  transport-specific  override,  where
       transport is the master.cf name of the message delivery transport.

default_filter_nexthop (default: empty)

       When  a  content_filter  or FILTER request specifies no explicit next-hop destination, use
       $default_filter_nexthop instead; when that value is empty, use the domain in the recipient
       address.   Specify  "default_filter_nexthop  = $myhostname" for compatibility with Postfix
       version  2.6  and  earlier,  or  specify  an  explicit  next-hop  destination  with   each
       content_filter value or FILTER action.

       This feature is available in Postfix 2.7 and later.

default_minimum_delivery_slots (default: 3)

       How  many  recipients  a  message must have in order to invoke the Postfix queue manager's
       scheduling algorithm at all.  Messages which would never accumulate  at  least  this  many
       delivery slots (subject to slot cost parameter as well) are never preempted.

       Use  transport_minimum_delivery_slots  to  specify  a  transport-specific  override, where
       transport is the master.cf name of the message delivery transport.

default_privs (default: nobody)

       The default rights used by the local(8) delivery agent for delivery to  external  file  or
       command.  These rights are used when delivery is requested from an aliases(5) file that is
       owned by root, or when delivery is done on behalf of root. DO  NOT  SPECIFY  A  PRIVILEGED
       USER OR THE POSTFIX OWNER.

default_process_limit (default: 100)

       The  default  maximal number of Postfix child processes that provide a given service. This
       limit can be overruled for specific services in the master.cf file.

default_rbl_reply (default: see postconf -d output)

       The default Postfix SMTP server response template for a request that  is  rejected  by  an
       RBL-based  restriction. This template can be overruled by specific entries in the optional
       rbl_reply_maps lookup table.

       This feature is available in Postfix 2.0 and later.

       The template is subject to exactly one level of $name substitution:

       $client
              The client hostname and IP address, formatted as name[address].

       $client_address
              The client IP address.

       $client_name
              The client hostname  or  "unknown".  See  reject_unknown_client_hostname  for  more
              details.

       $reverse_client_name
              The    client    hostname   from   address->name   lookup,   or   "unknown".    See
              reject_unknown_reverse_client_hostname for more details.

       $helo_name
              The hostname given in HELO or EHLO command or empty string.

       $rbl_class
              The blacklisted  entity  type:  Client  host,  Helo  command,  Sender  address,  or
              Recipient address.

       $rbl_code
              The  numerical  SMTP  response  code,  as  specified  with the maps_rbl_reject_code
              configuration parameter. Note: The numerical SMTP response code  is  required,  and
              must  appear  at  the  start  of the reply. With Postfix version 2.3 and later this
              information may be followed by an RFC 3463 enhanced status code.

       $rbl_domain
              The RBL domain where $rbl_what is blacklisted.

       $rbl_reason
              The reason why $rbl_what is blacklisted, or an empty string.

       $rbl_what
              The entity that is blacklisted (an IP address, a hostname, a  domain  name,  or  an
              email address whose domain was blacklisted).

       $recipient
              The recipient address or <> in case of the null address.

       $recipient_domain
              The recipient domain or empty string.

       $recipient_name
              The recipient address localpart or <> in case of null address.

       $sender
              The sender address or <> in case of the null address.

       $sender_domain
              The sender domain or empty string.

       $sender_name
              The sender address localpart or <> in case of the null address.

       ${name?text}
              Expands to `text' if $name is not empty.

       ${name:text}
              Expands to `text' if $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Note: when an enhanced status code is specified in an RBL reply template, it is subject to
       modification.  The following transformations are needed when the same RBL  reply  template
       is used for client, helo, sender, or recipient access restrictions.

       ·      When rejecting a sender address, the Postfix SMTP server will transform a recipient
              DSN status (e.g., 4.1.1-4.1.6) into the corresponding sender DSN status,  and  vice
              versa.

       ·      When  rejecting  non-address  information (such as the HELO command argument or the
              client hostname/address), the Postfix  SMTP  server  will  transform  a  sender  or
              recipient DSN status into a generic non-address DSN status (e.g., 4.0.0).

default_recipient_limit (default: 20000)

       The default per-transport upper limit on the number of in-memory recipients.  These limits
       take priority over the global qmgr_message_recipient_limit  after  the  message  has  been
       assigned  to  the  respective  transports.   See  also  default_extra_recipient_limit  and
       qmgr_message_recipient_minimum.

       Use transport_recipient_limit to specify a transport-specific override, where transport is
       the master.cf name of the message delivery transport.

default_recipient_refill_delay (default: 5s)

       The  default per-transport maximum delay between recipients refills.  When not all message
       recipients fit into the memory at once, keep loading more of them at least once every this
       many seconds.  This is used to make sure the recipients are refilled in timely manner even
       when $default_recipient_refill_limit is too high for too slow deliveries.

       Use transport_recipient_refill_delay  to  specify  a  transport-specific  override,  where
       transport is the master.cf name of the message delivery transport.

       This feature is available in Postfix 2.4 and later.

default_recipient_refill_limit (default: 100)

       The  default  per-transport  limit on the number of recipients refilled at once.  When not
       all message recipients fit into the memory at once, keep loading more of them  in  batches
       of  at  least  this  many  at a time.  See also $default_recipient_refill_delay, which may
       result in recipient batches lower than this when this limit  is  too  high  for  too  slow
       deliveries.

       Use  transport_recipient_refill_limit  to  specify  a  transport-specific  override, where
       transport is the master.cf name of the message delivery transport.

       This feature is available in Postfix 2.4 and later.

default_transport (default: smtp)

       The default mail delivery transport and next-hop destination for destinations that do  not
       match   $mydestination,   $inet_interfaces,   $proxy_interfaces,   $virtual_alias_domains,
       $virtual_mailbox_domains, or $relay_domains.  This information can be overruled  with  the
       sender_dependent_default_transport_maps parameter and with the transport(5) table.

       In   order   of   decreasing   precedence,   the   nexthop   destination   is  taken  from
       $sender_dependent_default_transport_maps,                              $default_transport,
       $sender_dependent_relayhost_maps, $relayhost, or from the recipient domain.

       Specify  a  string  of  the  form transport:nexthop, where transport is the name of a mail
       delivery transport defined in master.cf.  The :nexthop destination is optional; its syntax
       is documented in the manual page of the corresponding delivery agent.

       Example:

       default_transport = uucp:relayhostname

default_transport_rate_delay (default: 0s)

       The  default  amount of delay that is inserted between individual deliveries over the same
       message delivery transport, regardless of destination. If non-zero,  all  deliveries  over
       the same message delivery transport will happen one at a time.

       Use  transport_transport_rate_delay  to  specify  a transport-specific override, where the
       initial transport is the master.cf name of the message delivery transport.

       Example: throttle outbound SMTP mail to at most 3 deliveries per minute.

       /etc/postfix/main.cf:
           smtp_transport_rate_delay = 20s

       To enable the delay, specify a non-zero time value (an integral  value  plus  an  optional
       one-letter suffix that specifies the time unit).

       Time  units:  s  (seconds),  m (minutes), h (hours), d (days), w (weeks). The default time
       unit is s (seconds).

       NOTE: the delay is enforced by the queue manager.

       This feature is available in Postfix 3.1 and later.

default_verp_delimiters (default: +=)

       The two default VERP delimiter characters. These are used when no explicit delimiters  are
       specified  with  the  SMTP  XVERP  command  or with the "sendmail -V" command-line option.
       Specify characters that are allowed by the verp_delimiter_filter setting.

       This feature is available in Postfix 1.1 and later.

defer_code (default: 450)

       The numerical Postfix SMTP server response code when  a  remote  SMTP  client  request  is
       rejected by the "defer" restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

defer_service_name (default: defer)

       The  name  of  the  defer service. This service is implemented by the bounce(8) daemon and
       maintains a record of failed delivery attempts and generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

defer_transports (default: empty)

       The names of message delivery transports that  should  not  deliver  mail  unless  someone
       issues "sendmail -q" or equivalent. Specify zero or more names of mail delivery transports
       names that appear in the first field of master.cf.

       Example:

       defer_transports = smtp

delay_logging_resolution_limit (default: 2)

       The maximal number of digits after the decimal point when logging sub-second delay values.
       Specify a number in the range 0..6.

       Large  delay  values are rounded off to an integral number seconds; delay values below the
       delay_logging_resolution_limit are logged as "0", and delay values under 100s  are  logged
       with at most two-digit precision.

       The format of the "delays=a/b/c/d" logging is as follows:

       ·      a = time from message arrival to last active queue entry

       ·      b = time from last active queue entry to connection setup

       ·      c = time in connection setup, including DNS, EHLO and STARTTLS

       ·      d = time in message transmission

       This feature is available in Postfix 2.3 and later.

delay_notice_recipient (default: postmaster)

       The  recipient of postmaster notifications with the message headers of mail that cannot be
       delivered within $delay_warning_time time units.

       See also: delay_warning_time, notify_classes.

delay_warning_time (default: 0h)

       The time after which the sender receives a copy of the message headers  of  mail  that  is
       still  queued.  The  confirm_delay_cleared parameter controls sender notification when the
       delay clears up.

       To enable this feature, specify a non-zero time value (an integral value plus an  optional
       one-letter suffix that specifies the time unit).

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is h (hours).

       See also: delay_notice_recipient, notify_classes, confirm_delay_cleared.

deliver_lock_attempts (default: 20)

       The maximal number of attempts to acquire an exclusive lock on a mailbox file or bounce(8)
       logfile.

deliver_lock_delay (default: 1s)

       The  time  between  attempts  to  acquire an exclusive lock on a mailbox file or bounce(8)
       logfile.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

destination_concurrency_feedback_debug (default: no)

       Make the queue manager's feedback algorithm verbose for performance analysis purposes.

       This feature is available in Postfix 2.5 and later.

detect_8bit_encoding_header (default: yes)

       Automatically  detect  8BITMIME  body  content  by  looking  at Content-Transfer-Encoding:
       message headers; historically, this behavior was hard-coded to be "always on".

       This feature is available in Postfix 2.5 and later.

disable_dns_lookups (default: no)

       Disable DNS lookups in the Postfix SMTP and LMTP clients. When disabled, hosts are  looked
       up  with the getaddrinfo() system library routine which normally also looks in /etc/hosts.
       As of Postfix 2.11, this parameter is deprecated; use smtp_dns_support_level instead.

       DNS lookups are enabled by default.

disable_mime_input_processing (default: no)

       Turn off MIME processing while receiving mail. This means that  no  special  treatment  is
       given  to  Content-Type:  message  headers,  and  that  all text after the initial message
       headers is considered to be part of the message body.

       This feature is available in Postfix 2.0 and later.

       Mime input processing is enabled by default, and is needed  in  order  to  recognize  MIME
       headers in message content.

disable_mime_output_conversion (default: no)

       Disable  the  conversion  of  8BITMIME  format  to 7BIT format.  Mime output conversion is
       needed when the destination does not advertise 8BITMIME support.

       This feature is available in Postfix 2.0 and later.

disable_verp_bounces (default: no)

       Disable sending one bounce report per recipient.

       The default, one per recipient, is what ezmlm needs.

       This feature is available in Postfix 1.1 and later.

disable_vrfy_command (default: no)

       Disable the SMTP VRFY command. This stops some techniques used to harvest email addresses.

       Example:

       disable_vrfy_command = no

dns_ncache_ttl_fix_enable (default: no)

       Enable a workaround for future libc incompatibility. The  Postfix  implementation  of  RFC
       2308 negative reply caching relies on the promise that res_query() and res_search() invoke
       res_send(), which returns the server  response  in  an  application  buffer  even  if  the
       requested  record  does  not  exist.  If this promise is broken, specify "yes" to enable a
       workaround for DNS reputation lookups.

       This feature is available in Postfix 3.1 and later.

dnsblog_reply_delay (default: 0s)

       A debugging aid to artificially delay DNS responses.

       This feature is available in Postfix 2.8.

dnsblog_service_name (default: dnsblog)

       The name of  the  dnsblog(8)  service  entry  in  master.cf.  This  service  performs  DNS
       white/blacklist lookups.

       This feature is available in Postfix 2.8 and later.

dont_remove (default: 0)

       Don't  remove  queue  files  and save them to the "saved" mail queue.  This is a debugging
       aid.  To inspect the envelope information and content of a Postfix  queue  file,  use  the
       postcat(1) command.

double_bounce_sender (default: double-bounce)

       The  sender address of postmaster notifications that are generated by the mail system. All
       mail to this address is silently discarded, in order to terminate mail bounce loops.

duplicate_filter_limit (default: 1000)

       The maximal number of addresses remembered by the address duplicate filter for  aliases(5)
       or virtual(5) alias expansion, or for showq(8) queue displays.

empty_address_default_transport_maps_lookup_key (default: <>)

       The sender_dependent_default_transport_maps search string that will be used instead of the
       null sender address.

       This feature is available in Postfix 2.7 and later.

empty_address_recipient (default: MAILER-DAEMON)

       The recipient of mail addressed to  the  null  address.   Postfix  does  not  accept  such
       addresses  in  SMTP  commands,  but  they  may  still  be created locally as the result of
       configuration or software error.

empty_address_relayhost_maps_lookup_key (default: <>)

       The sender_dependent_relayhost_maps search string that will be used instead  of  the  null
       sender address.

       This   feature   is   available   in   Postfix  2.5  and  later.  With  earlier  versions,
       sender_dependent_relayhost_maps lookups were skipped for the null sender address.

enable_errors_to (default: no)

       Report mail delivery errors to the address  specified  with  the  non-standard  Errors-To:
       message  header,  instead  of  the  envelope  sender address (this feature is removed with
       Postfix version 2.2, is turned off by default with Postfix  version  2.1,  and  is  always
       turned on with older Postfix versions).

enable_idna2003_compatibility (default: no)

       Enable  'transitional'  compatibility between IDNA2003 and IDNA2008, when converting UTF-8
       domain names to/from the ASCII form that is  used  for  DNS  lookups.  Specify  "yes"  for
       compatibility with Postfix <= 3.1 (not recommended). This affects the conversion of domain
       names  that  contain  for   example   the   German   sz   and   the   Greek   zeta.    See
       http://unicode.org/cldr/utility/idna.jsp for more examples.

       This feature is available in Postfix 3.2 and later.

enable_long_queue_ids (default: no)

       Enable  long,  non-repeating,  queue IDs (queue file names).  The benefit of non-repeating
       names is simpler logfile analysis and easier queue migration (there  is  no  need  to  run
       "postsuper" to change queue file names that don't match their message file inode number).

       Note: see below for how to convert long queue file names to Postfix <= 2.8.

       Changing the parameter value to "yes" has the following effects:

       ·      Existing queue file names are not affected.

       ·      New  queue files are created with names such as 3Pt2mN2VXxznjll.  These are encoded
              in a 52-character alphabet that contains digits (0-9), upper-case letters (B-Z) and
              lower-case  letters  (b-z). For safety reasons the vowels (AEIOUaeiou) are excluded
              from the alphabet.  The name format is: 6  or  more  characters  for  the  time  in
              seconds,  4  characters for the time in microseconds, the 'z'; the remainder is the
              file inode number encoded in the first 51 characters of the 52-character alphabet.

       ·      New messages have a Message-ID header with queueID@myhostname.

       ·      The mailq (postqueue -p) output has  a  wider  Queue  ID  column.   The  number  of
              whitespace-separated fields is not changed.

       ·      The hash_queue_depth algorithm uses the first characters of the queue file creation
              time in  microseconds,  after  conversion  into  hexadecimal  representation.  This
              produces the same queue hashing behavior as if the queue file name was created with
              "enable_long_queue_ids = no".

       Changing the parameter value to "no" has the following effects:

       ·      Existing long queue file names  are  renamed  to  the  short  form  (while  running
              "postfix reload" or "postsuper").

       ·      New  queue  files  are  created  with  names such as C3CD21F3E90 from a hexadecimal
              alphabet that contains digits (0-9) and upper-case letters (A-F). The  name  format
              is:  5  characters  for  the  time in microseconds; the remainder is the file inode
              number.

       ·      New messages have a Message-ID header with YYYYMMDDHHMMSS.queueid@myhostname, where
              YYYYMMDDHHMMSS are the year, month, day, hour, minute and second.

       ·      The mailq (postqueue -p) output has the same format as with Postfix <= 2.8.

       ·      The  hash_queue_depth  algorithm  uses the first characters of the queue file name,
              with the hexadecimal representation of the file creation time in microseconds.

       Before migration to Postfix <= 2.8, the following commands are required  to  convert  long
       queue file names into short names:

       # postfix stop
       # postconf enable_long_queue_ids=no
       # postsuper

       Repeat the postsuper command until it reports no more queue file name changes.

       This feature is available in Postfix 2.9 and later.

enable_original_recipient (default: yes)

       Enable  support  for  the  original  recipient  address after an address is rewritten to a
       different address (for example with aliasing or with canonical mapping).

       The original recipient address is used as follows:

       Final delivery
              With "enable_original_recipient = yes", the original recipient address is stored in
              the  X-Original-To  message  header. This header may be used to distinguish between
              different recipients that share the same mailbox.

       Recipient deduplication
              With "enable_original_recipient = yes", the cleanup(8)  daemon  performs  duplicate
              recipient  elimination based on the content of (original recipient, maybe-rewritten
              recipient) pairs.  Otherwise, the cleanup(8) daemon  performs  duplicate  recipient
              elimination based only on the maybe-rewritten recipient address.

       Note:  with  Postfix  <=  3.2  the "setting enable_original_recipient = no" breaks address
       verification for addresses that are aliased or otherwise rewritten (Postfix is  unable  to
       store  the  address  verification  result  under  the  original probe destination address;
       instead, it can store the result only under the rewritten address).

       This feature is available in Postfix 2.1 and later. Postfix version 2.0 behaves as if this
       parameter  is  always  set  to  yes.   Postfix versions before 2.0 have no support for the
       original recipient address.

error_notice_recipient (default: postmaster)

       The recipient of postmaster notifications about mail delivery problems that are caused  by
       policy,  resource,  software or protocol errors.  These notifications are enabled with the
       notify_classes parameter.

error_service_name (default: error)

       The name of the error(8) pseudo delivery  agent.  This  service  always  returns  mail  as
       undeliverable.

       This feature is available in Postfix 2.0 and later.

execution_directory_expansion_filter (default: see postconf -d output)

       Restrict  the  characters  that  the local(8) delivery agent allows in $name expansions of
       $command_execution_directory.   Characters  outside  the  allowed  set  are  replaced   by
       underscores.

       This feature is available in Postfix 2.2 and later.

expand_owner_alias (default: no)

       When delivering to an alias "aliasname" that has an "owner-aliasname" companion alias, set
       the envelope sender address to the expansion of the  "owner-aliasname"  alias.   Normally,
       Postfix sets the envelope sender address to the name of the "owner-aliasname" alias.

export_environment (default: see postconf -d output)

       The  list  of  environment  variables  that  a  Postfix process will export to non-Postfix
       processes. The TZ variable is needed for sane time keeping on System-V-ish systems.

       Specify a list of names and/or name=value pairs, separated by whitespace or comma. Specify
       "{  name=value }" to protect whitespace or comma in parameter values (whitespace after "{"
       and before "}" is ignored). The form name=value is supported with Postfix version 2.1  and
       later; the use of {} is supported with Postfix 3.0 and later.

       Example:

       export_environment = TZ PATH=/bin:/usr/bin

extract_recipient_limit (default: 10240)

       The  maximal  number of recipient addresses that Postfix will extract from message headers
       when mail is submitted with "sendmail -t".

       This feature was removed in Postfix version 2.1.

fallback_relay (default: empty)

       Optional list of relay hosts for SMTP  destinations  that  can't  be  found  or  that  are
       unreachable. With Postfix 2.3 this parameter is renamed to smtp_fallback_relay.

       By  default,  mail is returned to the sender when a destination is not found, and delivery
       is deferred when a destination is unreachable.

       The fallback relays  must  be  SMTP  destinations.  Specify  a  domain,  host,  host:port,
       [host]:port,  [address]  or  [address]:port; the form [host] turns off MX lookups.  If you
       specify multiple SMTP destinations, Postfix will try them in the specified order.

       Note: before Postfix 2.2, do not use the fallback_relay feature when relaying mail  for  a
       backup  or  primary  MX  domain.  Mail  would  loop  between  the  Postfix MX host and the
       fallback_relay host when the final destination is unavailable.

       ·      In main.cf specify "relay_transport = relay",

       ·      In master.cf specify "-o fallback_relay =" (i.e., empty) at the end  of  the  relay
              entry.

       ·      In transport maps, specify "relay:nexthop..."  as the right-hand side for backup or
              primary MX domain entries.

       Postfix version 2.2 and later will not use the  fallback_relay  feature  for  destinations
       that it is MX host for.

fallback_transport (default: empty)

       Optional  message delivery transport that the local(8) delivery agent should use for names
       that are not found in the aliases(5) or UNIX password database.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,    mailbox_transport,    mailbox_command_maps,    mailbox_command,
       home_mailbox,  mail_spool_directory,   fallback_transport_maps,   fallback_transport   and
       luser_relay.

fallback_transport_maps (default: empty)

       Optional  lookup tables with per-recipient message delivery transports for recipients that
       the local(8) delivery agent could not find in the aliases(5) or UNIX password database.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,    mailbox_transport,    mailbox_command_maps,    mailbox_command,
       home_mailbox,  mail_spool_directory,   fallback_transport_maps,   fallback_transport   and
       luser_relay.

       For  safety  reasons,  this  feature  does  not  allow  $number  substitutions  in regular
       expression maps.

       This feature is available in Postfix 2.3 and later.

fast_flush_domains (default: $relay_domains)

       Optional list of destinations that are eligible for  per-destination  logfiles  with  mail
       that is queued to those destinations.

       By default, Postfix maintains "fast flush" logfiles only for destinations that the Postfix
       SMTP  server  is  willing  to  relay  to  (i.e.  the  default  is:  "fast_flush_domains  =
       $relay_domains"; see the relay_domains parameter in the postconf(5) manual).

       Specify  a  list of hosts or domains, "/file/name" patterns or "type:table" lookup tables,
       separated by commas and/or whitespace.  Continue long lines by starting the next line with
       whitespace.  A  "/file/name"  pattern  is  replaced by its contents; a "type:table" lookup
       table is matched when the domain or its parent domain appears as lookup key.

       Pattern  matching  of  domain  names  is  controlled  by  the  presence  or   absence   of
       "fast_flush_domains" in the parent_domain_matches_subdomains parameter value.

       Specify "fast_flush_domains =" (i.e., empty) to disable the feature altogether.

fast_flush_purge_time (default: 7d)

       The time after which an empty per-destination "fast flush" logfile is deleted.

       You  can  specify the time as a number, or as a number followed by a letter that indicates
       the time unit: s=seconds, m=minutes, h=hours, d=days, w=weeks.  The default time  unit  is
       days.

fast_flush_refresh_time (default: 12h)

       The  time after which a non-empty but unread per-destination "fast flush" logfile needs to
       be refreshed.  The contents of a logfile are  refreshed  by  requesting  delivery  of  all
       messages listed in the logfile.

       You  can  specify the time as a number, or as a number followed by a letter that indicates
       the time unit: s=seconds, m=minutes, h=hours, d=days, w=weeks.  The default time  unit  is
       hours.

fault_injection_code (default: 0)

       Force  specific  internal tests to fail, to test the handling of errors that are difficult
       to reproduce otherwise.

flush_service_name (default: flush)

       The name of the flush(8) service. This service maintains per-destination logfiles with the
       queue file names of mail that is queued for those destinations.

       This feature is available in Postfix 2.0 and later.

fork_attempts (default: 5)

       The maximal number of attempts to fork() a child process.

fork_delay (default: 1s)

       The delay between attempts to fork() a child process.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

forward_expansion_filter (default: see postconf -d output)

       Restrict the characters that the local(8) delivery agent allows  in  $name  expansions  of
       $forward_path.  Characters outside the allowed set are replaced by underscores.

forward_path (default: see postconf -d output)

       The  local(8)  delivery  agent search list for finding a .forward file with user-specified
       delivery methods. The first file that is found is used.

       The following $name expansions  are  done  on  forward_path  before  the  search  actually
       happens.  The  result  of  $name  expansion  is  filtered  with  the character set that is
       specified with the forward_expansion_filter parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
              The full recipient address.

       $extension
              The optional recipient address extension.

       $domain
              The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
              The address extension delimiter that was found in the  recipient  address  (Postfix
              2.11  and later), or the system-wide recipient address extension delimiter (Postfix
              2.10 and earlier).

       ${name?value}
              Expands to value when $name is non-empty.

       ${name:value}
              Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Examples:

       forward_path = /var/forward/$user
       forward_path =
           /var/forward/$user/.forward$recipient_delimiter$extension,
           /var/forward/$user/.forward

frozen_delivered_to (default: yes)

       Update  the  local(8)  delivery  agent's  idea   of   the   Delivered-To:   address   (see
       prepend_delivered_header) only once, at the start of a delivery attempt; do not update the
       Delivered-To: address while expanding aliases or .forward files.

       This feature is available in Postfix 2.3 and  later.  With  older  Postfix  releases,  the
       behavior  is  as  if  this parameter is set to "no". The old setting can be expensive with
       deeply nested aliases or .forward files. When  an  alias  or  .forward  file  changes  the
       Delivered-To:  address,  it  ties up one queue file and one cleanup process instance while
       mail is being forwarded.

hash_queue_depth (default: 1)

       The number of subdirectory levels for queue directories listed with  the  hash_queue_names
       parameter. Queue hashing is implemented by creating one or more levels of directories with
       one-character names.  Originally, these directory names were equal to the first characters
       of  the  queue file name, with the hexadecimal representation of the file creation time in
       microseconds.

       With long queue file names, queue hashing produces the same results as with  short  names.
       The  file  creation  time  in  microseconds  is converted into hexadecimal form before the
       result is used for queue hashing.  The base 16  encoding  gives  finer  control  over  the
       number  of  subdirectories  than  is possible with the base 52 encoding of long queue file
       names.

       After changing the hash_queue_names or hash_queue_depth  parameter,  execute  the  command
       "postfix reload".

hash_queue_names (default: deferred, defer)

       The names of queue directories that are split across multiple subdirectory levels.

       Before  Postfix  version  2.2, the default list of hashed queues was significantly larger.
       Claims about improvements in file system technology suggest that hashing of  the  incoming
       and  active  queues is no longer needed. Fewer hashed directories speed up the time needed
       to restart Postfix.

       After changing the hash_queue_names or hash_queue_depth  parameter,  execute  the  command
       "postfix reload".

header_address_token_limit (default: 10240)

       The maximal number of address tokens are allowed in an address message header. Information
       that exceeds the limit is discarded.  The limit is enforced by the cleanup(8) server.

header_checks (default: empty)

       Optional lookup tables for content inspection of  primary  non-MIME  message  headers,  as
       specified in the header_checks(5) manual page.

header_from_format (default: standard)

       The  format  of the Postfix-generated From: header. This setting affects the appearance of
       'full name' information when a local program such as /bin/mail submits a  message  without
       From: header through the Postfix sendmail(1) command.

       Specify one of the following:

       standard (default)
              Produce  a  header  formatted as "From: name <address>".  This is the default as of
              Postfix 3.3.

       obsolete
              Produce a header formatted as "From: address (name)". This is the behavior prior to
              Postfix 3.3.

       Notes:

       ·      Postfix  generates  the format "From: address" when name information is unavailable
              or the envelope sender address is empty. This is the  same  behavior  as  prior  to
              Postfix 3.3.

       ·      In the standard form, the name will be quoted if it contains specials as defined in
              RFC 5322, or the "!%" address operators.

       ·      The Postfix sendmail(1) command gets name  information  from  the  -F  command-line
              option, from the NAME environment variable, or from the UNIX password file.

       This feature is available in Postfix 3.3 and later.

header_size_limit (default: 102400)

       The  maximal  amount  of  memory  in  bytes  for storing a message header.  If a header is
       larger, the excess is discarded.  The limit is enforced by the cleanup(8) server.

helpful_warnings (default: yes)

       Log warnings about problematic configuration settings, and provide helpful suggestions.

       This feature is available in Postfix 2.0 and later.

home_mailbox (default: empty)

       Optional pathname of a mailbox file relative to a local(8) user's home directory.

       Specify a pathname ending in "/" for qmail-style delivery.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,    mailbox_transport,    mailbox_command_maps,    mailbox_command,
       home_mailbox,  mail_spool_directory,   fallback_transport_maps,   fallback_transport   and
       luser_relay.

       Examples:

       home_mailbox = Mailbox
       home_mailbox = Maildir/

hopcount_limit (default: 50)

       The  maximal  number  of Received:  message headers that is allowed in the primary message
       headers. A message that exceeds the limit is bounced, in order to stop a mailer loop.

html_directory (default: see postconf -d output)

       The location of Postfix HTML files that describe how to  build,  configure  or  operate  a
       specific Postfix subsystem or feature.

ignore_mx_lookup_error (default: no)

       Ignore  DNS  MX  lookups  that  produce  no response.  By default, the Postfix SMTP client
       defers delivery and tries again after some delay.  This behavior is required by  the  SMTP
       standard.

       Specify  "ignore_mx_lookup_error  =  yes"  to  force  a  DNS A record lookup instead. This
       violates the SMTP standard and can result in mis-delivery of mail.

import_environment (default: see postconf -d output)

       The list of environment parameters that a privileged Postfix process will  import  from  a
       non-Postfix  parent  process, or name=value environment overrides.  Unprivileged utilities
       will enforce the name=value  overrides,  but  otherwise  will  not  change  their  process
       environment.  Examples of relevant parameters:

       TZ     May be needed for sane time keeping on most System-V-ish systems.

       DISPLAY
              Needed for debugging Postfix daemons with an X-windows debugger.

       XAUTHORITY
              Needed for debugging Postfix daemons with an X-windows debugger.

       MAIL_CONFIG
              Needed to make "postfix -c" work.

       Specify a list of names and/or name=value pairs, separated by whitespace or comma. Specify
       "{ name=value }" to protect whitespace or comma in parameter values (whitespace after  "{"
       and  before "}" is ignored). The form name=value is supported with Postfix version 2.1 and
       later; the use of {} is supported with Postfix 3.0 and later.

in_flow_delay (default: 1s)

       Time to pause before accepting a new message, when the message arrival  rate  exceeds  the
       message delivery rate. This feature is turned on by default (it's disabled on SCO UNIX due
       to an SCO bug).

       With the default 100 Postfix SMTP server process limit, "in_flow_delay =  1s"  limits  the
       mail inflow to 100 messages per second above the number of messages delivered per second.

       Specify 0 to disable the feature. Valid delays are 0..10.

inet_interfaces (default: all)

       The  network  interface addresses that this mail system receives mail on. Specify "all" to
       receive mail on all network interfaces (default), and "loopback-only" to receive  mail  on
       loopback  network  interfaces  only  (Postfix  version 2.2 and later).  The parameter also
       controls delivery of mail to user@[ip.address].

       Note 1: you need to stop and start Postfix when this parameter changes.

       Note 2: address information may be enclosed inside [], but this form is not required here.

       When inet_interfaces specifies just one IPv4 and/or IPv6 address that is  not  a  loopback
       address,  the  Postfix  SMTP  client  will  use  this address as the IP source address for
       outbound mail. Support for IPv6 is available in Postfix version 2.2 and later.

       On a multi-homed firewall with separate Postfix instances listening on  the  "inside"  and
       "outside"  interfaces, this can prevent each instance from being able to reach remote SMTP
       servers on the "other side" of the firewall. Setting smtp_bind_address to  0.0.0.0  avoids
       the  potential  problem  for IPv4, and setting smtp_bind_address6 to :: solves the problem
       for IPv6.

       A better solution for multi-homed firewalls is to leave  inet_interfaces  at  the  default
       value  and  instead  use  explicit  IP addresses in the master.cf SMTP server definitions.
       This preserves the Postfix SMTP client's loop detection, by ensuring that each side of the
       firewall  knows that the other IP address is still the same host. Setting $inet_interfaces
       to a single IPv4 and/or IPV6 address is primarily useful with virtual hosting  of  domains
       on  secondary  IP  addresses,  when  each  IP address serves a different domain (and has a
       different $myhostname setting).

       See also the proxy_interfaces parameter, for  network  addresses  that  are  forwarded  to
       Postfix by way of a proxy or address translator.

       Examples:

       inet_interfaces = all (DEFAULT)
       inet_interfaces = loopback-only (Postfix version 2.2 and later)
       inet_interfaces = 127.0.0.1
       inet_interfaces = 127.0.0.1, [::1] (Postfix version 2.2 and later)
       inet_interfaces = 192.168.1.2, 127.0.0.1

inet_protocols (default: all)

       The  Internet  protocols Postfix will attempt to use when making or accepting connections.
       Specify one or more of "ipv4" or "ipv6", separated by whitespace or commas. The form "all"
       is  equivalent  to  "ipv4,  ipv6"  or  "ipv4",  depending  on whether the operating system
       implements IPv6.

       With Postfix 2.8 and earlier the default is "ipv4". For backwards compatibility with these
       releases,  the Postfix 2.9 and later upgrade procedure appends an explicit "inet_protocols
       = ipv4" setting to main.cf  when  no  explicit  setting  is  present.  This  compatibility
       workaround will be phased out as IPv6 deployment becomes more common.

       This feature is available in Postfix 2.2 and later.

       Note: you MUST stop and start Postfix after changing this parameter.

       On  systems  that pre-date IPV6_V6ONLY support (RFC 3493), an IPv6 server will also accept
       IPv4 connections, even when IPv4 is turned off  with  the  inet_protocols  parameter.   On
       systems  with  IPV6_V6ONLY  support, Postfix will use separate server sockets for IPv6 and
       IPv4, and each will accept only connections for the corresponding protocol.

       When IPv4 support is enabled via the inet_protocols parameter, Postfix will  look  up  DNS
       type  A  records,  and  will  convert IPv4-in-IPv6 client IP addresses (::ffff:1.2.3.4) to
       their original IPv4  form  (1.2.3.4).   The  latter  is  needed  on  hosts  that  pre-date
       IPV6_V6ONLY support (RFC 3493).

       When  IPv6  support  is enabled via the inet_protocols parameter, Postfix will do DNS type
       AAAA record lookups.

       When both IPv4 and IPv6 support are enabled, the  Postfix  SMTP  client  will  choose  the
       protocol  as specified with the smtp_address_preference parameter. Postfix versions before
       2.8 attempt to connect via IPv6 before attempting to use IPv4.

       Examples:

       inet_protocols = ipv4
       inet_protocols = all (DEFAULT)
       inet_protocols = ipv6
       inet_protocols = ipv4, ipv6

initial_destination_concurrency (default: 5)

       The  initial  per-destination  concurrency  level  for  parallel  delivery  to  the   same
       destination.   With  per-destination  recipient  limit  >  1,  a  destination is a domain,
       otherwise it is a recipient.

       Use transport_initial_destination_concurrency to specify  a  transport-specific  override,
       where  transport  is the master.cf name of the message delivery transport (Postfix 2.5 and
       later).

       Warning: with concurrency of 1, one bad message can be enough to block all mail to a site.

internal_mail_filter_classes (default: empty)

       What categories of Postfix-generated mail are subject to before-queue  content  inspection
       by  non_smtpd_milters,  header_checks  and  body_checks.   Specify  zero  or  more  of the
       following, separated by whitespace or comma.

       bounce Inspect the content of delivery status notifications.

       notify Inspect the content  of  postmaster  notifications  by  the  smtp(8)  and  smtpd(8)
              processes.

       NOTE:  It's  generally  not  safe  to enable content inspection of Postfix-generated email
       messages. The user is warned.

       This feature is available in Postfix 2.3 and later.

invalid_hostname_reject_code (default: 501)

       The numerical Postfix SMTP server response code when  the  client  HELO  or  EHLO  command
       parameter is rejected by the reject_invalid_helo_hostname restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

ipc_idle (default: version dependent)

       The  time after which a client closes an idle internal communication channel.  The purpose
       is to allow Postfix daemon processes to terminate voluntarily after they become idle. This
       is used, for example, by the Postfix address resolving and rewriting clients.

       With Postfix 2.4 the default value was reduced from 100s to 5s.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

ipc_timeout (default: 3600s)

       The time limit for  sending  or  receiving  information  over  an  internal  communication
       channel.   The  purpose  is  to  break  out  of  deadlock situations. If the time limit is
       exceeded the software aborts with a fatal error.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

ipc_ttl (default: 1000s)

       The  time  after  which  a  client  closes  an active internal communication channel.  The
       purpose is to allow Postfix daemon processes to terminate voluntarily after reaching their
       client  limit.   This is used, for example, by the Postfix address resolving and rewriting
       clients.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

line_length_limit (default: 2048)

       Upon  input,  long lines are chopped up into pieces of at most this length; upon delivery,
       long lines are reconstructed.

lmdb_map_size (default: 16777216)

       The initial OpenLDAP LMDB database size limit in bytes.   Each  time  a  database  becomes
       full, its size limit is doubled.

       This feature is available in Postfix 2.11 and later.

lmtp_address_preference (default: ipv6)

       The  LMTP-specific  version  of  the smtp_address_preference configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_address_verify_target (default: rcpt)

       The LMTP-specific version of the smtp_address_verify_target configuration parameter.   See
       there for details.

       This feature is available in Postfix 3.0 and later.

lmtp_assume_final (default: no)

       When  a remote LMTP server announces no DSN support, assume that the server performs final
       delivery, and send "delivered" delivery status notifications  instead  of  "relayed".  The
       default setting is backwards compatible to avoid the infinitesimal possibility of breaking
       existing LMTP-based content filters.

lmtp_balance_inet_protocols (default: yes)

       The LMTP-specific version of the smtp_balance_inet_protocols configuration parameter.  See
       there for details.

       This feature is available in Postfix 3.3 and later.

lmtp_bind_address (default: empty)

       The LMTP-specific version of the smtp_bind_address configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_bind_address6 (default: empty)

       The LMTP-specific version of the smtp_bind_address6 configuration  parameter.   See  there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_body_checks (default: empty)

       The  LMTP-specific  version of the smtp_body_checks configuration parameter. See there for
       details.

       This feature is available in Postfix 2.5 and later.

lmtp_cache_connection (default: yes)

       Keep Postfix LMTP client connections open for up  to  $max_idle  seconds.  When  the  LMTP
       client receives a request for the same connection the connection is reused.

       This  parameter is available in Postfix version 2.2 and earlier.  With Postfix version 2.3
       and later,  see  lmtp_connection_cache_on_demand,  lmtp_connection_cache_destinations,  or
       lmtp_connection_reuse_time_limit.

       The  effectiveness  of  cached connections will be determined by the number of remote LMTP
       servers in use, and the concurrency limit specified for the Postfix  LMTP  client.  Cached
       connections are closed under any of the following conditions:

       ·      The  Postfix  LMTP client idle time limit is reached.  This limit is specified with
              the Postfix max_idle configuration parameter.

       ·      A delivery request specifies a different destination than the one currently cached.

       ·      The per-process limit on the number of delivery requests is reached.  This limit is
              specified with the Postfix max_use configuration parameter.

       ·      Upon  the onset of another delivery request, the remote LMTP server associated with
              the current session does not respond to the RSET command.

       Most of these limitations have been with the Postfix a connection  cache  that  is  shared
       among multiple LMTP client programs.

lmtp_cname_overrides_servername (default: yes)

       The  LMTP-specific version of the smtp_cname_overrides_servername configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connect_timeout (default: 0s)

       The Postfix LMTP client time limit for completing a  TCP  connection,  or  zero  (use  the
       operating  system  built-in  time  limit).   When  no  connection  can  be made within the
       deadline, the LMTP client tries the next address on the mail exchanger list.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

       Example:

       lmtp_connect_timeout = 30s

lmtp_connection_cache_destinations (default: empty)

       The   LMTP-specific   version   of  the  smtp_connection_cache_destinations  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_on_demand (default: yes)

       The LMTP-specific version of the smtp_connection_cache_on_demand configuration  parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_time_limit (default: 2s)

       The LMTP-specific version of the smtp_connection_cache_time_limit configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_reuse_count_limit (default: 0)

       The  LMTP-specific  version   of   the   smtp_connection_reuse_count_limit   configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_connection_reuse_time_limit (default: 300s)

       The LMTP-specific version of the smtp_connection_reuse_time_limit configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_data_done_timeout (default: 600s)

       The Postfix LMTP client time limit for sending the LMTP ".", and for receiving the  remote
       LMTP  server  response.   When  no  response is received within the deadline, a warning is
       logged that the mail may be delivered multiple times.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_data_init_timeout (default: 120s)

       The  Postfix  LMTP  client time limit for sending the LMTP DATA command, and for receiving
       the remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_data_xfer_timeout (default: 180s)

       The  Postfix  LMTP  client  time  limit  for  sending  the LMTP message content.  When the
       connection stalls for more than $lmtp_data_xfer_timeout the  LMTP  client  terminates  the
       transfer.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

lmtp_defer_if_no_mx_address_found (default: no)

       The  LMTP-specific  version   of   the   smtp_defer_if_no_mx_address_found   configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_delivery_status_filter (default: empty)

       The LMTP-specific version of the smtp_delivery_status_filter configuration parameter.  See
       there for details.

       This feature is available in Postfix 3.0 and later.

lmtp_destination_concurrency_limit (default: $default_destination_concurrency_limit)

       The maximal number of parallel deliveries to the same destination  via  the  lmtp  message
       delivery  transport.  This  limit  is  enforced by the queue manager. The message delivery
       transport name is the first field in the entry in the master.cf file.

lmtp_destination_recipient_limit (default: $default_destination_recipient_limit)

       The maximal number of recipients per message for the lmtp message delivery transport. This
       limit  is  enforced by the queue manager. The message delivery transport name is the first
       field in the entry in the master.cf file.

       Setting   this   parameter   to   a    value    of    1    changes    the    meaning    of
       lmtp_destination_concurrency_limit  from  concurrency  per  domain  into  concurrency  per
       recipient.

lmtp_discard_lhlo_keyword_address_maps (default: empty)

       Lookup tables, indexed by the remote LMTP server address, with case insensitive  lists  of
       LHLO  keywords (pipelining, starttls, auth, etc.) that the Postfix LMTP client will ignore
       in the LHLO response  from  a  remote  LMTP  server.  See  lmtp_discard_lhlo_keywords  for
       details.    The    table    is    not   indexed   by   hostname   for   consistency   with
       smtpd_discard_ehlo_keyword_address_maps.

       This feature is available in Postfix 2.3 and later.

lmtp_discard_lhlo_keywords (default: empty)

       A case insensitive list of LHLO keywords  (pipelining,  starttls,  auth,  etc.)  that  the
       Postfix LMTP client will ignore in the LHLO response from a remote LMTP server.

       This feature is available in Postfix 2.3 and later.

       Notes:

       ·      Specify the silent-discard pseudo keyword to prevent this action from being logged.

       ·      Use  the  lmtp_discard_lhlo_keyword_address_maps  feature  to discard LHLO keywords
              selectively.

lmtp_dns_reply_filter (default: empty)

       Optional filter for Postfix LMTP client DNS lookup results.  See smtp_dns_reply_filter for
       details including an example.

       This feature is available in Postfix 3.0 and later.

lmtp_dns_resolver_options (default: empty)

       The  LMTP-specific  version of the smtp_dns_resolver_options configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_dns_support_level (default: empty)

       The LMTP-specific version of  the  smtp_dns_support_level  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_enforce_tls (default: no)

       The  LMTP-specific version of the smtp_enforce_tls configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_fallback_relay (default: empty)

       Optional list of relay hosts for LMTP  destinations  that  can't  be  found  or  that  are
       unreachable.  In main.cf elements are separated by whitespace or commas.

       By  default,  mail is returned to the sender when a destination is not found, and delivery
       is deferred when a destination is unreachable.

       The fallback relays must be TCP destinations, specified without a leading "inet:"  prefix.
       Specify a host or host:port.  Since MX lookups do not apply with LMTP, there is no need to
       use the "[host]" or "[host]:port" forms.   If  you  specify  multiple  LMTP  destinations,
       Postfix will try them in the specified order.

       This feature is available in Postfix 3.1 and later.

lmtp_generic_maps (default: empty)

       The LMTP-specific version of the smtp_generic_maps configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_header_checks (default: empty)

       The LMTP-specific version of the smtp_header_checks configuration parameter. See there for
       details.

       This feature is available in Postfix 2.5 and later.

lmtp_host_lookup (default: dns)

       The  LMTP-specific version of the smtp_host_lookup configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_name (default: $myhostname)

       The hostname to send in the LMTP LHLO command.

       The default value is the machine hostname.  Specify a hostname or [ip.add.re.ss].

       This information can be specified in the main.cf file for all LMTP clients, or it  can  be
       specified in the master.cf file for a specific client, for example:

           /etc/postfix/master.cf:
               mylmtp ... lmtp -o lmtp_lhlo_name=foo.bar.com

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_timeout (default: 300s)

       The  Postfix  LMTP  client  time limit for sending the LHLO command, and for receiving the
       initial remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_line_length_limit (default: 990)

       The  LMTP-specific  version  of  the  smtp_line_length_limit configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mail_timeout (default: 300s)

       The Postfix LMTP client time limit for sending the MAIL FROM command,  and  for  receiving
       the remote LMTP server response.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

lmtp_mime_header_checks (default: empty)

       The LMTP-specific version of  the  smtp_mime_header_checks  configuration  parameter.  See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_mx_address_limit (default: 5)

       The LMTP-specific version of the smtp_mx_address_limit configuration parameter.  See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mx_session_limit (default: 2)

       The LMTP-specific version of the smtp_mx_session_limit configuration parameter.  See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_nested_header_checks (default: empty)

       The  LMTP-specific  version  of the smtp_nested_header_checks configuration parameter. See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_per_record_deadline (default: no)

       The LMTP-specific version of the smtp_per_record_deadline  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.9 and later.

lmtp_pix_workaround_delay_time (default: 10s)

       The  LMTP-specific  version of the smtp_pix_workaround_delay_time configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workaround_maps (default: empty)

       The LMTP-specific version of the smtp_pix_workaround_maps  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.4 and later.

lmtp_pix_workaround_threshold_time (default: 500s)

       The   LMTP-specific   version   of  the  smtp_pix_workaround_threshold_time  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workarounds (default: empty)

       The LMTP-specific version of the smtp_pix_workaround configuration parameter.   See  there
       for details.

       This feature is available in Postfix 2.4 and later.

lmtp_quit_timeout (default: 300s)

       The  Postfix  LMTP  client  time limit for sending the QUIT command, and for receiving the
       remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_quote_rfc821_envelope (default: yes)

       The  LMTP-specific version of the smtp_quote_rfc821_envelope configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_randomize_addresses (default: yes)

       The LMTP-specific version of the smtp_randomize_addresses  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_rcpt_timeout (default: 300s)

       The  Postfix LMTP client time limit for sending the RCPT TO command, and for receiving the
       remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_reply_filter (default: empty)

       The LMTP-specific version of the smtp_reply_filter configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.7 and later.

lmtp_rset_timeout (default: 20s)

       The Postfix LMTP client time limit for sending the RSET command,  and  for  receiving  the
       remote  LMTP  server  response.  The LMTP client sends RSET in order to finish a recipient
       address probe, or to verify that a cached connection is still alive.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

lmtp_sasl_auth_cache_name (default: empty)

       The  LMTP-specific  version of the smtp_sasl_auth_cache_name configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_cache_time (default: 90d)

       The LMTP-specific version of the smtp_sasl_auth_cache_time configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_enable (default: no)

       Enable SASL authentication in the Postfix LMTP client.

lmtp_sasl_auth_soft_bounce (default: yes)

       The  LMTP-specific version of the smtp_sasl_auth_soft_bounce configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_mechanism_filter (default: empty)

       The LMTP-specific version of the smtp_sasl_mechanism_filter configuration parameter.   See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_password_maps (default: empty)

       Optional  Postfix  LMTP  client lookup tables with one username:password entry per host or
       domain.  If a remote host or domain has no username:password entry, then the Postfix  LMTP
       client will not attempt to authenticate to the remote host.

lmtp_sasl_path (default: empty)

       Implementation-specific   information   that   is  passed  through  to  the  SASL  plug-in
       implementation that is selected with lmtp_sasl_type.  Typically this specifies the name of
       a configuration file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_security_options (default: noplaintext, noanonymous)

       SASL  security  options;  as  of Postfix 2.3 the list of available features depends on the
       SASL client implementation that is selected with lmtp_sasl_type.

       The following security features are defined for the cyrus client SASL implementation:

       noplaintext
              Disallow authentication methods that use plaintext passwords.

       noactive
              Disallow authentication  methods  that  are  vulnerable  to  non-dictionary  active
              attacks.

       nodictionary
              Disallow authentication methods that are vulnerable to passive dictionary attack.

       noanonymous
              Disallow anonymous logins.

       Example:

       lmtp_sasl_security_options = noplaintext

lmtp_sasl_tls_security_options (default: $lmtp_sasl_security_options)

       The  LMTP-specific  version of the smtp_sasl_tls_security_options configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_tls_verified_security_options (default: $lmtp_sasl_tls_security_options)

       The LMTP-specific version  of  the  smtp_sasl_tls_verified_security_options  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_type (default: cyrus)

       The  SASL  plug-in  type  that the Postfix LMTP client should use for authentication.  The
       available types are listed with the "postconf -A" command.

       This feature is available in Postfix 2.3 and later.

lmtp_send_dummy_mail_auth (default: no)

       The LMTP-specific version of the smtp_send_dummy_mail_auth configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.9 and later.

lmtp_send_xforward_command (default: no)

       Send  an  XFORWARD  command  to  the remote LMTP server when the LMTP LHLO server response
       announces XFORWARD support.  This allows an  lmtp(8)  delivery  agent,  used  for  content
       filter  message  injection,  to  forward  the name, address, protocol and HELO name of the
       original client to the content filter and downstream  queuing  LMTP  server.   Before  you
       change  the  value  to yes, it is best to make sure that your content filter supports this
       command.

       This feature is available in Postfix 2.1 and later.

lmtp_sender_dependent_authentication (default: no)

       The  LMTP-specific  version  of  the  smtp_sender_dependent_authentication   configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_5xx_greeting (default: yes)

       The  LMTP-specific  version  of  the  smtp_skip_5xx_greeting configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_quit_response (default: no)

       Wait for the response to the LMTP QUIT command.

lmtp_starttls_timeout (default: 300s)

       The LMTP-specific version of the smtp_starttls_timeout configuration parameter.  See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tcp_port (default: 24)

       The  default  TCP  port that the Postfix LMTP client connects to.  Specify a symbolic name
       (see services(5)) or a numeric port.

lmtp_tls_CAfile (default: empty)

       The LMTP-specific version of the smtp_tls_CAfile configuration parameter.  See  there  for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_CApath (default: empty)

       The  LMTP-specific  version of the smtp_tls_CApath configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_block_early_mail_reply (default: empty)

       The LMTP-specific version of the smtp_tls_block_early_mail_reply configuration  parameter.
       See there for details.

       This feature is available in Postfix 2.7 and later.

lmtp_tls_cert_file (default: empty)

       The  LMTP-specific  version  of the smtp_tls_cert_file configuration parameter.  See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_ciphers (default: medium)

       The LMTP-specific version of the smtp_tls_ciphers configuration parameter. See  there  for
       details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_dcert_file (default: empty)

       The  LMTP-specific  version of the smtp_tls_dcert_file configuration parameter.  See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_dkey_file (default: $lmtp_tls_dcert_file)

       The LMTP-specific version of the smtp_tls_dkey_file configuration  parameter.   See  there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_eccert_file (default: empty)

       The  LMTP-specific version of the smtp_tls_eccert_file configuration parameter.  See there
       for details.

       This feature is available in Postfix 2.6 and later, when Postfix is  compiled  and  linked
       with OpenSSL 1.0.0 or later.

lmtp_tls_eckey_file (default: empty)

       The  LMTP-specific  version of the smtp_tls_eckey_file configuration parameter.  See there
       for details.

       This feature is available in Postfix 2.6 and later, when Postfix is  compiled  and  linked
       with OpenSSL 1.0.0 or later.

lmtp_tls_enforce_peername (default: yes)

       The  LMTP-specific  version of the smtp_tls_enforce_peername configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_exclude_ciphers (default: empty)

       The LMTP-specific version of the smtp_tls_exclude_ciphers  configuration  parameter.   See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_fingerprint_cert_match (default: empty)

       The  LMTP-specific version of the smtp_tls_fingerprint_cert_match configuration parameter.
       See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_fingerprint_digest (default: md5)

       The LMTP-specific version of the smtp_tls_fingerprint_digest configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_force_insecure_host_tlsa_lookup (default: no)

       The  LMTP-specific  version  of the smtp_tls_force_insecure_host_tlsa_lookup configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_tls_key_file (default: $lmtp_tls_cert_file)

       The LMTP-specific version of the smtp_tls_key_file configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_loglevel (default: 0)

       The LMTP-specific version of the smtp_tls_loglevel configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_ciphers (default: medium)

       The LMTP-specific version of the smtp_tls_mandatory_ciphers configuration parameter.   See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_exclude_ciphers (default: empty)

       The   LMTP-specific   version   of  the  smtp_tls_mandatory_exclude_ciphers  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_protocols (default: !SSLv2, !SSLv3)

       The LMTP-specific version of the smtp_tls_mandatory_protocols configuration parameter. See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_note_starttls_offer (default: no)

       The  LMTP-specific  version  of  the smtp_tls_note_starttls_offer configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_per_site (default: empty)

       The LMTP-specific version of the smtp_tls_per_site configuration parameter.  See there for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_policy_maps (default: empty)

       The  LMTP-specific  version of the smtp_tls_policy_maps configuration parameter. See there
       for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_protocols (default: !SSLv2, !SSLv3)

       The LMTP-specific version of the smtp_tls_protocols configuration parameter. See there for
       details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_scert_verifydepth (default: 9)

       The  LMTP-specific version of the smtp_tls_scert_verifydepth configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_secure_cert_match (default: nexthop)

       The LMTP-specific version of the smtp_tls_secure_cert_match configuration  parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_security_level (default: empty)

       The  LMTP-specific  version  of  the smtp_tls_security_level configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_database (default: empty)

       The LMTP-specific version of the smtp_tls_session_cache_database configuration  parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_timeout (default: 3600s)

       The  LMTP-specific  version of the smtp_tls_session_cache_timeout configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_trust_anchor_file (default: empty)

       The LMTP-specific version of the smtp_tls_trust_anchor_file configuration parameter.   See
       there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_tls_verify_cert_match (default: hostname)

       The  LMTP-specific  version of the smtp_tls_verify_cert_match configuration parameter. See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_use_tls (default: no)

       The LMTP-specific version of the smtp_use_tls  configuration  parameter.   See  there  for
       details.

       This feature is available in Postfix 2.3 and later.

lmtp_xforward_timeout (default: 300s)

       The Postfix LMTP client time limit for sending the XFORWARD command, and for receiving the
       remote LMTP server response.

       In case of problems the client does NOT try the next address on the mail exchanger list.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

local_command_shell (default: empty)

       Optional  shell  program  for  local(8)  delivery  to  non-Postfix  command.   By default,
       non-Postfix commands are executed directly; commands are given to  given  to  the  default
       shell  (typically, /bin/sh) only when they contain shell meta characters or shell built-in
       commands.

       "sendmail's restricted shell" (smrsh) is what most people will use in  order  to  restrict
       what  programs  can  be  run  from  e.g.  .forward  files  (smrsh  is part of the Sendmail
       distribution).

       Note: when a shell program is specified, it is invoked even when the command  contains  no
       shell built-in commands or meta characters.

       Example:

       local_command_shell = /some/where/smrsh -c
       local_command_shell = /bin/bash -c

local_delivery_status_filter (default: $default_delivery_status_filter)

       Optional  filter  for the local(8) delivery agent to change the status code or explanatory
       text of successful or unsuccessful  deliveries.   See  default_delivery_status_filter  for
       details.

       This feature is available in Postfix 3.0 and later.

local_destination_concurrency_limit (default: 2)

       The  maximal  number  of  parallel deliveries via the local mail delivery transport to the
       same recipient (when "local_destination_recipient_limit = 1") or  the  maximal  number  of
       parallel  deliveries  to  the same local domain (when "local_destination_recipient_limit >
       1"). This limit is enforced by the queue manager. The message delivery transport  name  is
       the first field in the entry in the master.cf file.

       A  low limit of 2 is recommended, just in case someone has an expensive shell command in a
       .forward file or in an alias (e.g., a mailing list manager).  You don't want to  run  lots
       of those at the same time.

local_destination_recipient_limit (default: 1)

       The  maximal  number  of  recipients  per  message  delivery  via  the local mail delivery
       transport. This limit is enforced by the queue manager.  The  message  delivery  transport
       name is the first field in the entry in the master.cf file.

       Setting    this    parameter    to    a    value    >    1    changes   the   meaning   of
       local_destination_concurrency_limit from concurrency per recipient  into  concurrency  per
       domain.

local_header_rewrite_clients (default: permit_inet_interfaces)

       Rewrite  message  header  addresses  in  mail  from  these  clients  and update incomplete
       addresses with the domain name in $myorigin or $mydomain;  either  don't  rewrite  message
       headers  from  other  clients  at  all,  or  rewrite message headers and update incomplete
       addresses with the domain specified in the remote_header_rewrite_domain parameter.

       See the append_at_myorigin and append_dot_mydomain parameters for details  of  how  domain
       names are appended to incomplete addresses.

       Specify a list of zero or more of the following:

       permit_inet_interfaces
              Append the domain name in $myorigin or $mydomain when the client IP address matches
              $inet_interfaces. This is enabled by default.

       permit_mynetworks
              Append the domain name in $myorigin or $mydomain when the client IP address matches
              any network or network address listed in $mynetworks. This setting will not prevent
              remote mail header address rewriting when mail from a remote client is forwarded by
              a neighboring system.

       permit_sasl_authenticated
              Append  the  domain  name in $myorigin or $mydomain when the client is successfully
              authenticated via the RFC 4954 (AUTH) protocol.

       permit_tls_clientcerts
              Append the domain name in $myorigin or $mydomain when the remote  SMTP  client  TLS
              certificate fingerprint or public key fingerprint (Postfix 2.9 and later) is listed
              in $relay_clientcerts.  The fingerprint digest algorithm is  configurable  via  the
              smtpd_tls_fingerprint_digest  parameter (hard-coded as md5 prior to Postfix version
              2.5).

       permit_tls_all_clientcerts
              Append the domain name in $myorigin or $mydomain when the remote  SMTP  client  TLS
              certificate  is  successfully  verified,  regardless of whether it is listed on the
              server, and regardless of the certifying authority.

       check_address_map type:table

       type:table
              Append the domain name in $myorigin or $mydomain when the client IP address matches
              the  specified lookup table.  The lookup result is ignored, and no subnet lookup is
              done. This is suitable for, e.g., pop-before-smtp lookup tables.

       Examples:

       The Postfix < 2.2 backwards compatible setting: always rewrite message headers, and always
       append my own domain to incomplete header addresses.

           local_header_rewrite_clients = static:all

       The  purist  (and default) setting: rewrite headers only in mail from Postfix sendmail and
       in SMTP mail from this machine.

           local_header_rewrite_clients = permit_inet_interfaces

       The intermediate setting: rewrite header  addresses  and  append  $myorigin  or  $mydomain
       information  only  with mail from Postfix sendmail, from local clients, or from authorized
       SMTP clients.

       Note: this setting will not prevent remote mail header address rewriting when mail from  a
       remote client is forwarded by a neighboring system.

           local_header_rewrite_clients = permit_mynetworks,
               permit_sasl_authenticated permit_tls_clientcerts
               check_address_map hash:/etc/postfix/pop-before-smtp

local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps)

       Lookup  tables  with  all  names  or addresses of local recipients: a recipient address is
       local when its  domain  matches  $mydestination,  $inet_interfaces  or  $proxy_interfaces.
       Specify  @domain  as  a  wild-card  for  domains  that do not have a valid recipient list.
       Technically, tables listed with $local_recipient_maps are used as lists: Postfix needs  to
       know  only  if  a lookup string is found or not, but it does not use the result from table
       lookup.

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.  Tables
       will be searched in the specified order until a match is found.

       If  this  parameter  is  non-empty (the default), then the Postfix SMTP server will reject
       mail for unknown local users.

       To  turn  off  local  recipient   checking   in   the   Postfix   SMTP   server,   specify
       "local_recipient_maps =" (i.e. empty).

       The  default  setting  assumes  that  you use the default Postfix local delivery agent for
       local delivery. You need to update the local_recipient_maps setting if:

       ·      You redefine the local delivery agent in master.cf.

       ·      You redefine the "local_transport" setting in main.cf.

       ·      You use the "luser_relay", "mailbox_transport", or "fallback_transport" feature  of
              the Postfix local(8) delivery agent.

       Details are described in the LOCAL_RECIPIENT_README file.

       Beware:  if  the Postfix SMTP server runs chrooted, you need to access the passwd file via
       the proxymap(8) service, in order to overcome chroot access restrictions. The alternative,
       maintaining a copy of the system password file in the chroot jail is not practical.

       Examples:

       local_recipient_maps =

local_transport (default: local:$myhostname)

       The default mail delivery transport and next-hop destination for final delivery to domains
       listed with mydestination, and for [ipaddress] destinations that match $inet_interfaces or
       $proxy_interfaces.  This information can be overruled with the transport(5) table.

       By  default,  local  mail  is delivered to the transport called "local", which is just the
       name of a service that is defined the master.cf file.

       Specify a string of the form transport:nexthop, where transport is  the  name  of  a  mail
       delivery transport defined in master.cf.  The :nexthop destination is optional; its syntax
       is documented in the manual page of the corresponding delivery agent.

       Beware: if you override the default local delivery agent  then  you  need  to  review  the
       LOCAL_RECIPIENT_README  document,  otherwise  the  SMTP  server  may reject mail for local
       recipients.

luser_relay (default: empty)

       Optional catch-all destination for unknown local(8)  recipients.   By  default,  mail  for
       unknown   recipients   in   domains   that   match   $mydestination,  $inet_interfaces  or
       $proxy_interfaces is returned as undeliverable.

       The following $name expansions are done on luser_relay:

       $domain
              The recipient domain.

       $extension
              The recipient address extension.

       $home  The recipient's home directory.

       $local The entire recipient address localpart.

       $recipient
              The full recipient address.

       $recipient_delimiter
              The address extension delimiter that was found in the  recipient  address  (Postfix
              2.11  and later), or the system-wide recipient address extension delimiter (Postfix
              2.10 and earlier).

       $shell The recipient's login shell.

       $user  The recipient username.

       ${name?value}
              Expands to value when $name has a non-empty value.

       ${name:value}
              Expands to value when $name has an empty value.

       Instead of $name you can also specify ${name} or $(name).

       Note: luser_relay works only for the Postfix local(8) delivery agent.

       Note: if you use this feature for accounts not in the UNIX password file,  then  you  must
       specify  "local_recipient_maps  =" (i.e. empty) in the main.cf file, otherwise the Postfix
       SMTP server will reject mail for non-UNIX accounts with "User unknown in  local  recipient
       table".

       Examples:

       luser_relay = $user@other.host
       luser_relay = $local@other.host
       luser_relay = admin+$local

mail_name (default: Postfix)

       The  mail system name that is displayed in Received: headers, in the SMTP greeting banner,
       and in bounced mail.

mail_owner (default: postfix)

       The UNIX system account that owns the Postfix queue and  most  Postfix  daemon  processes.
       Specify  the  name  of an unprivileged user account that does not share a user or group ID
       with other accounts, and that owns  no  other  files  or  processes  on  the  system.   In
       particular, don't specify nobody or daemon.  PLEASE USE A DEDICATED USER ID AND GROUP ID.

       When  this  parameter  value is changed you need to re-run "postfix set-permissions" (with
       Postfix version 2.0 and earlier: "/etc/postfix/post-install set-permissions".

mail_release_date (default: see postconf -d output)

       The Postfix release date, in "YYYYMMDD" format.

mail_spool_directory (default: see postconf -d output)

       The directory where local(8) UNIX-style mailboxes are kept. The default setting depends on
       the system type. Specify a name ending in / for maildir-style delivery.

       Note:  maildir  delivery  is  done  with  the privileges of the recipient.  If you use the
       mail_spool_directory setting  for  maildir  style  delivery,  then  you  must  create  the
       top-level maildir directory in advance. Postfix will not create it.

       Examples:

       mail_spool_directory = /var/mail
       mail_spool_directory = /var/spool/mail

mail_version (default: see postconf -d output)

       The  version  of  the  mail  system.  Stable  releases  are  named major.minor.patchlevel.
       Experimental releases also include the release date. The version string can  be  used  in,
       for example, the SMTP greeting banner.

mailbox_command (default: empty)

       Optional  external  command  that  the  local(8)  delivery  agent  should  use for mailbox
       delivery.  The command is run with the user ID and the primary group ID privileges of  the
       recipient.   Exception: command delivery for root executes with $default_privs privileges.
       This is not a problem, because 1) mail for root should always be aliased to  a  real  user
       and 2) don't log in as root, use "su" instead.

       The following environment variables are exported to the command:

       CLIENT_ADDRESS
              Remote client network address. Available in Postfix version 2.2 and later.

       CLIENT_HELO
              Remote client EHLO command parameter. Available in Postfix version 2.2 and later.

       CLIENT_HOSTNAME
              Remote client hostname. Available in Postfix version 2.2 and later.

       CLIENT_PROTOCOL
              Remote client protocol. Available in Postfix version 2.2 and later.

       DOMAIN The domain part of the recipient address.

       EXTENSION
              The optional address extension.

       HOME   The recipient home directory.

       LOCAL  The recipient address localpart.

       LOGNAME
              The recipient's username.

       ORIGINAL_RECIPIENT
              The entire recipient address, before any address rewriting or aliasing.

       RECIPIENT
              The full recipient address.

       SASL_METHOD
              SASL  authentication  method specified in the remote client AUTH command. Available
              in Postfix version 2.2 and later.

       SASL_SENDER
              SASL sender address specified in the remote client MAIL FROM command. Available  in
              Postfix version 2.2 and later.

       SASL_USER
              SASL  username  specified  in the remote client AUTH command.  Available in Postfix
              version 2.2 and later.

       SENDER The full sender address.

       SHELL  The recipient's login shell.

       USER   The recipient username.

       Unlike other Postfix  configuration  parameters,  the  mailbox_command  parameter  is  not
       subjected  to  $name substitutions. This is to make it easier to specify shell syntax (see
       example below).

       If you can, avoid shell meta  characters  because  they  will  force  Postfix  to  run  an
       expensive shell process. If you're delivering via Procmail then running a shell won't make
       a noticeable difference in the total cost.

       Note: if you use the mailbox_command feature to deliver mail system-wide, you must set  up
       an alias that forwards mail for root to a real user.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,    mailbox_transport,    mailbox_command_maps,    mailbox_command,
       home_mailbox,   mail_spool_directory,   fallback_transport_maps,   fallback_transport  and
       luser_relay.

       Examples:

       mailbox_command = /some/where/procmail
       mailbox_command = /some/where/procmail -a "$EXTENSION"
       mailbox_command = /some/where/maildrop -d "$USER"
               -f "$SENDER" "$EXTENSION"

mailbox_command_maps (default: empty)

       Optional lookup tables with per-recipient external commands to use  for  local(8)  mailbox
       delivery.  Behavior is as with mailbox_command.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,    mailbox_transport,    mailbox_command_maps,    mailbox_command,
       home_mailbox,   mail_spool_directory,   fallback_transport_maps,   fallback_transport  and
       luser_relay.

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.  Tables
       will be searched in the specified order until a match is found.

mailbox_delivery_lock (default: see postconf -d output)

       How  to  lock  a  UNIX-style  local(8)  mailbox before attempting delivery.  For a list of
       available file locking methods, use the "postconf -l" command.

       This setting is ignored with maildir style delivery,  because  such  deliveries  are  safe
       without explicit locks.

       Note:  The  dotlock  method requires that the recipient UID or GID has write access to the
       parent directory of the mailbox file.

       Note: the default setting of this parameter is system dependent.

mailbox_size_limit (default: 51200000)

       The maximal size of any local(8) individual mailbox or maildir file, or zero  (no  limit).
       In  fact,  this  limits  the  size  of  any  file  that is written to upon local delivery,
       including files written by external commands that are executed by  the  local(8)  delivery
       agent.

       This limit must not be smaller than the message size limit.

mailbox_transport (default: empty)

       Optional  message  delivery  transport  that  the  local(8)  delivery agent should use for
       mailbox delivery to all local recipients, whether or not they are found in the UNIX passwd
       database.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,    mailbox_transport,    mailbox_command_maps,    mailbox_command,
       home_mailbox,   mail_spool_directory,   fallback_transport_maps,   fallback_transport  and
       luser_relay.

mailbox_transport_maps (default: empty)

       Optional lookup tables with per-recipient message delivery transports to use for  local(8)
       mailbox delivery, whether or not the recipients are found in the UNIX passwd database.

       The precedence of local(8) delivery features from high to low is: aliases, .forward files,
       mailbox_transport_maps,    mailbox_transport,    mailbox_command_maps,    mailbox_command,
       home_mailbox,   mail_spool_directory,   fallback_transport_maps,   fallback_transport  and
       luser_relay.

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.  Tables
       will be searched in the specified order until a match is found.

       For  safety  reasons,  this  feature  does  not  allow  $number  substitutions  in regular
       expression maps.

       This feature is available in Postfix 2.3 and later.

mailq_path (default: see postconf -d output)

       Sendmail compatibility feature that  specifies  where  the  Postfix  mailq(1)  command  is
       installed. This command can be used to list the Postfix mail queue.

manpage_directory (default: see postconf -d output)

       Where the Postfix manual pages are installed.

maps_rbl_domains (default: empty)

       Obsolete feature: use the reject_rbl_client feature instead.

maps_rbl_reject_code (default: 554)

       The  numerical  Postfix  SMTP  server  response  code when a remote SMTP client request is
       blocked  by  the  reject_rbl_client,   reject_rhsbl_client,   reject_rhsbl_reverse_client,
       reject_rhsbl_sender or reject_rhsbl_recipient restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

masquerade_classes (default: envelope_sender, header_sender, header_recipient)

       What addresses are subject to address masquerading.

       By  default,  address  masquerading is limited to envelope sender addresses, and to header
       sender and header recipient addresses.  This allows you to use address masquerading  on  a
       mail gateway while still being able to forward mail to users on individual machines.

       Specify   zero   or   more   of:   envelope_sender,   envelope_recipient,   header_sender,
       header_recipient

masquerade_domains (default: empty)

       Optional list of  domains  whose  subdomain  structure  will  be  stripped  off  in  email
       addresses.

       The list is processed left to right, and processing stops at the first match.  Thus,

           masquerade_domains = foo.example.com example.com

       strips    "user@any.thing.foo.example.com"    to    "user@foo.example.com",   but   strips
       "user@any.thing.else.example.com" to "user@example.com".

       A domain name prefixed with ! means do not masquerade this domain or its subdomains. Thus,

           masquerade_domains = !foo.example.com example.com

       does not change "user@any.thing.foo.example.com"  or  "user@foo.example.com",  but  strips
       "user@any.thing.else.example.com" to "user@example.com".

       Note:  with  Postfix  version  2.2,  message header address masquerading happens only when
       message header address rewriting is enabled:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The   message   is    received    from    a    network    client    that    matches
              $local_header_rewrite_clients,

       ·      The  message  is  received  from  the network, and the remote_header_rewrite_domain
              parameter specifies a non-empty value.

       To get the behavior before Postfix version 2.2,  specify  "local_header_rewrite_clients  =
       static:all".

       Example:

       masquerade_domains = $mydomain

masquerade_exceptions (default: empty)

       Optional  list  of  user  names  that are not subjected to address masquerading, even when
       their address matches $masquerade_domains.

       By default, address masquerading makes no exceptions.

       Specify a list of user names, "/file/name" or "type:table" patterns, separated  by  commas
       and/or  whitespace.  The  list is matched left to right, and the search stops on the first
       match. A "/file/name" pattern is replaced by its contents; a "type:table" lookup table  is
       matched  when  a  name matches a lookup key (the lookup result is ignored).  Continue long
       lines by starting the next line with whitespace. Specify "!pattern" to exclude a name from
       the list. The form "!/file/name" is supported only in Postfix version 2.4 and later.

       Examples:

       masquerade_exceptions = root, mailer-daemon
       masquerade_exceptions = root

master_service_disable (default: empty)

       Selectively  disable master(8) listener ports by service type or by service name and type.
       Specify a list of service types ("inet", "unix", "fifo", or "pass") or "name/type" tuples,
       where "name" is the first field of a master.cf entry and "type" is a service type. As with
       other Postfix matchlists, a search stops  at  the  first  match.   Specify  "!pattern"  to
       exclude a service from the list. By default, all master(8) listener ports are enabled.

       Note:  this  feature  does  not support "/file/name" or "type:table" patterns, nor does it
       support wildcards such as "*" or "all". This is intentional.

       Examples:

       # With Postfix 2.6..2.10 use '.' instead of '/'.
       # Turn on all master(8) listener ports (the default).
       master_service_disable =
       # Turn off only the main SMTP listener port.
       master_service_disable = smtp/inet
       # Turn off all TCP/IP listener ports.
       master_service_disable = inet
       # Turn off all TCP/IP listener ports except "foo".
       master_service_disable = !foo/inet, inet

       This feature is available in Postfix 2.6 and later.

max_idle (default: 100s)

       The maximum amount of time that an idle Postfix  daemon  process  waits  for  an  incoming
       connection before terminating voluntarily.  This parameter is ignored by the Postfix queue
       manager and by other long-lived Postfix daemon processes.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

max_use (default: 100)

       The  maximal  number  of  incoming  connections that a Postfix daemon process will service
       before terminating voluntarily.  This parameter is ignored by the  Postfix  queue  manager
       and by other long-lived Postfix daemon processes.

maximal_backoff_time (default: 4000s)

       The maximal time between attempts to deliver a deferred message.

       This  parameter  should  be set to a value greater than or equal to $minimal_backoff_time.
       See also $queue_run_delay.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

maximal_queue_lifetime (default: 5d)

       Consider  a  message as undeliverable, when delivery fails with a temporary error, and the
       time in the queue has reached the maximal_queue_lifetime limit.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is d (days).

       Specify 0 when mail delivery should be tried only once.

message_drop_headers (default: bcc, content-length, resent-bcc, return-path)

       Names   of  message  headers  that  the  cleanup(8)  daemon  will  remove  after  applying
       header_checks(5)  and  before  invoking  Milter  applications.   The  default  setting  is
       compatible with Postfix < 3.0.

       Specify  a  list  of  header  names,  separated by comma or space.  Names are matched in a
       case-insensitive manner.  The list of supported header names is limited only by  available
       memory.

       This feature is available in Postfix 3.0 and later.

message_reject_characters (default: empty)

       The  set  of  characters  that  Postfix  will reject in message content.  The usual C-like
       escape sequences are recognized: \a \b \f \n \r \t \v \ddd (up to three octal digits)  and
       \\.

       Note  1: this feature does not recognize text that requires MIME decoding. It inspects raw
       message content, just like header_checks and body_checks.

       Note 2: this feature is disabled with "receive_override_options = no_header_body_checks".

       Example:

       message_reject_characters = \0

       This feature is available in Postfix 2.3 and later.

message_size_limit (default: 10240000)

       The maximal size in bytes of a message, including envelope information.

       Note: be careful when making changes.  Excessively small values will result in the loss of
       non-delivery  notifications,  when a bounce message size exceeds the local or remote MTA's
       message size limit.

message_strip_characters (default: empty)

       The set of characters that Postfix will remove from message  content.   The  usual  C-like
       escape  sequences are recognized: \a \b \f \n \r \t \v \ddd (up to three octal digits) and
       \\.

       Note 1: this feature does not recognize text that requires MIME decoding. It inspects  raw
       message content, just like header_checks and body_checks.

       Note 2: this feature is disabled with "receive_override_options = no_header_body_checks".

       Example:

       message_strip_characters = \0

       This feature is available in Postfix 2.3 and later.

meta_directory (default: see 'postconf -d' output)

       The  location  of  non-executable  files that are shared among multiple Postfix instances,
       such as postfix-files, dynamicmaps.cf, and the multi-instance template files main.cf.proto
       and   master.cf.proto.    This   directory  should  contain  only  Postfix-related  files.
       Typically, the meta_directory parameter has  the  same  default  as  the  config_directory
       parameter (/etc/postfix or /usr/local/etc/postfix).

       For  backwards  compatibility  with  Postfix versions 2.6..2.11, specify "meta_directory =
       $daemon_directory"  in  main.cf  before  installing  or  upgrading  Postfix,  or   specify
       "meta_directory  =  /path/name"  on the "make makefiles", "make install" or "make upgrade"
       command line.

       This feature is available in Postfix 3.0 and later.

milter_command_timeout (default: 30s)

       The time limit for sending an SMTP command to a Milter (mail filter) application, and  for
       receiving the response.

       Specify  a  non-zero time value (an integral value plus an optional one-letter suffix that
       specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w  (weeks).  The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_connect_macros (default: see postconf -d output)

       The  macros that are sent to Milter (mail filter) applications after completion of an SMTP
       connection. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_connect_timeout (default: 30s)

       The time limit for connecting to a Milter (mail filter) application, and  for  negotiating
       protocol options.

       Specify  a  non-zero time value (an integral value plus an optional one-letter suffix that
       specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w  (weeks).  The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_content_timeout (default: 300s)

       The  time limit for sending message content to a Milter (mail filter) application, and for
       receiving the response.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies the time unit).

       Time  units:  s  (seconds),  m (minutes), h (hours), d (days), w (weeks). The default time
       unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_data_macros (default: see postconf -d output)

       The macros that are sent to version 4 or higher Milter (mail  filter)  applications  after
       the  SMTP  DATA  command.  See MILTER_README for a list of available macro names and their
       meanings.

       This feature is available in Postfix 2.3 and later.

milter_default_action (default: tempfail)

       The  default  action  when  a  Milter  (mail  filter)  application   is   unavailable   or
       mis-configured. Specify one of the following:

       accept Proceed as if the mail filter was not present.

       reject Reject all further commands in this session with a permanent status code.

       tempfail
              Reject all further commands in this session with a temporary status code.

       quarantine
              Like  "accept",  but freeze the message in the "hold" queue. Available with Postfix
              2.6 and later.

       This feature is available in Postfix 2.3 and later.

milter_end_of_data_macros (default: see postconf -d output)

       The macros  that  are  sent  to  Milter  (mail  filter)  applications  after  the  message
       end-of-data. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_end_of_header_macros (default: see postconf -d output)

       The macros that are sent to Milter (mail filter) applications after the end of the message
       header. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.5 and later.

milter_header_checks (default: empty)

       Optional lookup tables for content inspection of message  headers  that  are  produced  by
       Milter  applications.   See the header_checks(5) manual page available actions. Currently,
       PREPEND is not implemented.

       The following example sends all mail that is marked as SPAM to a  spam  handling  machine.
       Note that matches are case-insensitive by default.

       /etc/postfix/main.cf:
           milter_header_checks = pcre:/etc/postfix/milter_header_checks

       /etc/postfix/milter_header_checks:
           /^X-SPAM-FLAG:\s+YES/ FILTER mysmtp:sanitizer.example.com:25

       The  milter_header_checks  mechanism  could  also be used for whitelisting. For example it
       could be used to skip heavy content inspection for DKIM-signed mail  from  known  friendly
       domains.

       This feature is available in Postfix 2.7, and as an optional patch for Postfix 2.6.

milter_helo_macros (default: see postconf -d output)

       The  macros that are sent to Milter (mail filter) applications after the SMTP HELO or EHLO
       command. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_macro_daemon_name (default: $myhostname)

       The {daemon_name} macro value for Milter (mail filter)  applications.   See  MILTER_README
       for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_macro_defaults (default: empty)

       Optional  list  of  name=value pairs that specify default values for arbitrary macros that
       Postfix may send to Milter applications.   These  defaults  are  used  when  there  is  no
       corresponding information from the message delivery context.

       Specify name=value or {name}=value pairs separated by comma or whitespace.  Enclose a pair
       in "{}" when a value contains comma or whitespace (this form ignores whitespace after  the
       enclosing "{", around the "=", and before the enclosing "}").

       This feature is available in Postfix 3.1 and later.

milter_macro_v (default: $mail_name $mail_version)

       The  {v}  macro value for Milter (mail filter) applications.  See MILTER_README for a list
       of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_mail_macros (default: see postconf -d output)

       The macros that are sent to Milter (mail filter) applications after  the  SMTP  MAIL  FROM
       command. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_protocol (default: 6)

       The mail filter protocol version and optional protocol extensions for communication with a
       Milter application; prior to Postfix 2.6 the default protocol is  2.  Postfix  sends  this
       version  number during the initial protocol handshake.  It should match the version number
       that is expected by the mail filter application (or by its Milter library).

       Protocol versions:

       2      Use Sendmail 8 mail filter protocol version 2 (default with Sendmail  version  8.11
              .. 8.13 and Postfix version 2.3 ..  2.5).

       3      Use Sendmail 8 mail filter protocol version 3.

       4      Use Sendmail 8 mail filter protocol version 4.

       6      Use  Sendmail  8 mail filter protocol version 6 (default with Sendmail version 8.14
              and Postfix version 2.6).

       Protocol extensions:

       no_header_reply
              Specify this when the Milter application will not reply for each individual message
              header.

       This feature is available in Postfix 2.3 and later.

milter_rcpt_macros (default: see postconf -d output)

       The  macros  that  are  sent  to  Milter (mail filter) applications after the SMTP RCPT TO
       command. See MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_unknown_command_macros (default: see postconf -d output)

       The macros that are sent to version 3 or higher Milter (mail filter) applications after an
       unknown  SMTP  command.   See  MILTER_README for a list of available macro names and their
       meanings.

       This feature is available in Postfix 2.3 and later.

mime_boundary_length_limit (default: 2048)

       The maximal length of MIME multipart boundary strings. The MIME  processor  is  unable  to
       distinguish    between    boundary   strings   that   do   not   differ   in   the   first
       $mime_boundary_length_limit characters.

       This feature is available in Postfix 2.0 and later.

mime_header_checks (default: $header_checks)

       Optional lookup tables  for  content  inspection  of  MIME  related  message  headers,  as
       described in the header_checks(5) manual page.

       This feature is available in Postfix 2.0 and later.

mime_nesting_limit (default: 100)

       The  maximal  recursion  level  that the MIME processor will handle.  Postfix refuses mail
       that is nested deeper than the specified limit.

       This feature is available in Postfix 2.0 and later.

minimal_backoff_time (default: 300s)

       The minimal time between attempts to deliver a deferred message; prior to Postfix 2.4  the
       default value was 1000s.

       This  parameter also limits the time an unreachable destination is kept in the short-term,
       in-memory, destination status cache.

       This parameter should  be  set  greater  than  or  equal  to  $queue_run_delay.  See  also
       $maximal_backoff_time.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

multi_instance_directories (default: empty)

       An optional list of  non-default  Postfix  configuration  directories;  these  directories
       belong  to  additional  Postfix  instances  that  share  the  Postfix executable files and
       documentation with the default Postfix instance, and  that  are  started,  stopped,  etc.,
       together  with  the  default  Postfix  instance.  Specify a list of pathnames separated by
       comma or whitespace.

       When $multi_instance_directories is empty, the postfix(1) command runs in  single-instance
       mode  and  operates  on  a single Postfix instance only. Otherwise, the postfix(1) command
       runs in multi-instance mode and invokes the  multi-instance  manager  specified  with  the
       multi_instance_wrapper  parameter.  The multi-instance manager in turn executes postfix(1)
       commands   for   the   default   instance   and   for    all    Postfix    instances    in
       $multi_instance_directories.

       Currently, this parameter setting is ignored except for the default main.cf file.

       This feature is available in Postfix 2.6 and later.

multi_instance_enable (default: no)

       Allow this Postfix instance to be started, stopped, etc., by a multi-instance manager.  By
       default, new instances are created in a safe state that prevents them from  being  started
       inadvertently.  This parameter is reserved for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_group (default: empty)

       The   optional   instance  group  name  of  this  Postfix  instance.  A  group  identifies
       closely-related Postfix instances that the multi-instance manager can start,  stop,  etc.,
       as a unit.  This parameter is reserved for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_name (default: empty)

       The  optional  instance  name of this Postfix instance. This name becomes also the default
       value for the syslog_name parameter.

       This feature is available in Postfix 2.6 and later.

multi_instance_wrapper (default: empty)

       The pathname of a multi-instance manager command that the postfix(1) command invokes  when
       the  multi_instance_directories parameter value is non-empty. The pathname may be followed
       by initial command arguments separated by whitespace; shell metacharacters such as  quotes
       are not supported in this context.

       The  postfix(1) command invokes the manager command with the postfix(1) non-option command
       arguments on the manager command line, and with all installation configuration  parameters
       exported into the manager command process environment. The manager command in turn invokes
       the postfix(1) command for individual Postfix instances as  "postfix  -c  config_directory
       command".

       This feature is available in Postfix 2.6 and later.

multi_recipient_bounce_reject_code (default: 550)

       The  numerical  Postfix  SMTP  server  response  code when a remote SMTP client request is
       blocked by the reject_multi_recipient_bounce restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.1 and later.

mydestination (default: $myhostname, localhost.$mydomain, localhost)

       The list of domains that are delivered via the $local_transport mail  delivery  transport.
       By  default  this  is the Postfix local(8) delivery agent which looks up all recipients in
       /etc/passwd  and  /etc/aliases.  The  SMTP  server  validates  recipient  addresses   with
       $local_recipient_maps and rejects non-existent recipients. See also the local domain class
       in the ADDRESS_CLASS_README file.

       The default mydestination value specifies names for the local machine  only.   On  a  mail
       domain gateway, you should also include $mydomain.

       The   $local_transport   delivery   method   is   also  selected  for  mail  addressed  to
       user@[the.net.work.address] of the mail  system  (the  IP  addresses  specified  with  the
       inet_interfaces and proxy_interfaces parameters).

       Warnings:

       ·      Do  not  specify  the  names  of  virtual  domains  -  those  domains are specified
              elsewhere. See VIRTUAL_README for more information.

       ·      Do not specify the names of domains that this machine is backup MX  host  for.  See
              STANDARD_CONFIGURATION_README for how to set up backup MX hosts.

       ·      By default, the Postfix SMTP server rejects mail for recipients not listed with the
              local_recipient_maps parameter.  See the postconf(5) manual for  a  description  of
              the local_recipient_maps and unknown_local_recipient_reject_code parameters.

       Specify  a  list of host or domain names, "/file/name" or "type:table" patterns, separated
       by commas and/or whitespace. A  "/file/name"  pattern  is  replaced  by  its  contents;  a
       "type:table"  lookup  table is matched when a name matches a lookup key (the lookup result
       is ignored).  Continue long lines by starting the next line with whitespace.

       Examples:

       mydestination = $myhostname, localhost.$mydomain $mydomain
       mydestination = $myhostname, localhost.$mydomain www.$mydomain, ftp.$mydomain

mydomain (default: see postconf -d output)

       The internet domain name of this mail system.  The default is to use $myhostname minus the
       first component, or "localdomain" (Postfix 2.3 and later).  $mydomain is used as a default
       value for many other configuration parameters.

       Example:

       mydomain = domain.tld

myhostname (default: see postconf -d output)

       The internet hostname of this mail system. The  default  is  to  use  the  fully-qualified
       domain  name  (FQDN)  from gethostname(), or to use the non-FQDN result from gethostname()
       and append  ".$mydomain".   $myhostname  is  used  as  a  default  value  for  many  other
       configuration parameters.

       Example:

       myhostname = host.example.com

mynetworks (default: see postconf -d output)

       The list of "trusted" remote SMTP clients that have more privileges than "strangers".

       In  particular, "trusted" SMTP clients are allowed to relay mail through Postfix.  See the
       smtpd_relay_restrictions parameter description in the postconf(5) manual.

       You can specify the list of "trusted" network addresses by hand or you can let Postfix  do
       it  for you (which is the default).  See the description of the mynetworks_style parameter
       for more information.

       If you specify the mynetworks list by hand, Postfix ignores the mynetworks_style setting.

       Specify a list of network addresses  or  network/netmask  patterns,  separated  by  commas
       and/or whitespace. Continue long lines by starting the next line with whitespace.

       The  netmask  specifies the number of bits in the network part of a host address.  You can
       also specify "/file/name" or "type:table" patterns.  A "/file/name" pattern is replaced by
       its  contents;  a "type:table" lookup table is matched when a table entry matches a lookup
       string (the lookup result is ignored).

       The list is matched left to right, and the search  stops  on  the  first  match.   Specify
       "!pattern" to exclude an address or network block from the list. The form "!/file/name" is
       supported only in Postfix version 2.4 and later.

       Note 1: Pattern matching of domain names is controlled by the or absence  of  "mynetworks"
       in the parent_domain_matches_subdomains parameter value.

       Note  2:  IP  version  6 address information must be specified inside [] in the mynetworks
       value, and in files specified with "/file/name".  IP version 6 addresses contain  the  ":"
       character, and would otherwise be confused with a "type:table" pattern.

       Examples:

       mynetworks = 127.0.0.0/8 168.100.189.0/28
       mynetworks = !192.168.0.1, 192.168.0.0/28
       mynetworks = 127.0.0.0/8 168.100.189.0/28 [::1]/128 [2001:240:587::]/64
       mynetworks = $config_directory/mynetworks
       mynetworks = hash:/etc/postfix/network_table

mynetworks_style (default: Postfix >= 3.0: host, Postfix < 3.0: subnet)

       The  method  to generate the default value for the mynetworks parameter.  This is the list
       of trusted networks for relay access control etc.

       ·      Specify "mynetworks_style = host"  when  Postfix  should  "trust"  only  the  local
              machine.

       ·      Specify "mynetworks_style = subnet" when Postfix should "trust" remote SMTP clients
              in the same IP subnetworks as the local machine.  On Linux,  this  works  correctly
              only with interfaces specified with the "ifconfig" command.

       ·      Specify  "mynetworks_style = class" when Postfix should "trust" remote SMTP clients
              in the same IP class A/B/C networks as the local machine.  Caution: this may  cause
              Postfix  to  "trust"  your entire provider's network.  Instead, specify an explicit
              mynetworks list by hand, as described with the mynetworks configuration parameter.

myorigin (default: $myhostname)

       The domain name that locally-posted mail appears to come from,  and  that  locally  posted
       mail is delivered to. The default, $myhostname, is adequate for small sites.  If you run a
       domain with multiple machines, you should (1) change this to $mydomain and (2)  set  up  a
       domain-wide alias database that aliases each user to user@that.users.mailhost.

       Example:

       myorigin = $mydomain

nested_header_checks (default: $header_checks)

       Optional  lookup  tables  for  content  inspection of non-MIME message headers in attached
       messages, as described in the header_checks(5) manual page.

       This feature is available in Postfix 2.0 and later.

newaliases_path (default: see postconf -d output)

       Sendmail compatibility feature that specifies the location of the  newaliases(1)  command.
       This command can be used to rebuild the local(8) aliases(5) database.

non_fqdn_reject_code (default: 504)

       The  numerical  Postfix  SMTP  server  reply code when a client request is rejected by the
       reject_non_fqdn_helo_hostname,   reject_non_fqdn_sender    or    reject_non_fqdn_recipient
       restriction.

non_smtpd_milters (default: empty)

       A  list  of  Milter  (mail  filter) applications for new mail that does not arrive via the
       Postfix smtpd(8) server. This includes local submission via the sendmail(1) command  line,
       new  mail  that  arrives via the Postfix qmqpd(8) server, and old mail that is re-injected
       into the queue with "postsuper  -r".   Specify  space  or  comma  as  separator.  See  the
       MILTER_README document for details.

       This feature is available in Postfix 2.3 and later.

notify_classes (default: resource, software)

       The  list  of  error classes that are reported to the postmaster. The default is to report
       only the most serious problems. The paranoid may wish to turn on the policy (UCE and  mail
       relaying) and protocol error (broken mail software) reports.

       NOTE: postmaster notifications may contain confidential information such as SASL passwords
       or message content.  It  is  the  system  administrator's  responsibility  to  treat  such
       information with care.

       The error classes are:

       bounce (also implies 2bounce)
              Send  the postmaster copies of the headers of bounced mail, and send transcripts of
              SMTP sessions when Postfix rejects mail. The notification is sent  to  the  address
              specified   with  the  bounce_notice_recipient  configuration  parameter  (default:
              postmaster).

       2bounce
              Send undeliverable bounced mail to the postmaster. The notification is sent to  the
              address   specified   with  the  2bounce_notice_recipient  configuration  parameter
              (default: postmaster).

       data   Send the postmaster a transcript of the  SMTP  session  with  an  error  because  a
              critical  data  file  was  unavailable.  The  notification  is  sent to the address
              specified  with  the  error_notice_recipient  configuration   parameter   (default:
              postmaster).
              This feature is available in Postfix 2.9 and later.

       delay  Send the postmaster copies of the headers of delayed mail (see delay_warning_time).
              The notification is sent to the address specified with  the  delay_notice_recipient
              configuration parameter (default: postmaster).

       policy Send  the  postmaster  a  transcript  of the SMTP session when a client request was
              rejected because of (UCE) policy. The notification is sent to the address specified
              with the error_notice_recipient configuration parameter (default: postmaster).

       protocol
              Send  the  postmaster  a transcript of the SMTP session in case of client or server
              protocol errors. The notification  is  sent  to  the  address  specified  with  the
              error_notice_recipient configuration parameter (default: postmaster).

       resource
              Inform  the  postmaster  of  mail  not  delivered  due  to  resource problems.  The
              notification is sent to  the  address  specified  with  the  error_notice_recipient
              configuration parameter (default: postmaster).

       software
              Inform  the  postmaster  of  mail  not  delivered  due  to  software problems.  The
              notification is sent to  the  address  specified  with  the  error_notice_recipient
              configuration parameter (default: postmaster).

       Examples:

       notify_classes = bounce, delay, policy, protocol, resource, software
       notify_classes = 2bounce, resource, software

nullmx_reject_code (default: 556)

       The  numerical  reply  code  when  the  Postfix  SMTP server rejects a sender or recipient
       address because its domain has a nullmx DNS record (an MX record with an empty  hostname).
       This is one of the possible replies from the restrictions reject_unknown_sender_domain and
       reject_unknown_recipient_domain.

       This feature is available in Postfix 3.0 and later.

openssl_path (default: openssl)

       The location of the OpenSSL command line program openssl(1).  This is used by the "postfix
       tls"   command   to   create  private  keys,  certificate  signing  requests,  self-signed
       certificates, and to compute public key digests for DANE TLSA records.  In  multi-instance
       environments,  this  parameter  is always determined from the configuration of the default
       Postfix instance.

       Example:

           /etc/postfix/main.cf:
               # NetBSD pkgsrc:
               openssl_path = /usr/pkg/bin/openssl
               # Local build:
               openssl_path = /usr/local/bin/openssl

       This feature is available in Postfix 3.1 and later.

owner_request_special (default: yes)

       Enable special treatment for owner-listname entries in  the  aliases(5)  file,  and  don't
       split  owner-listname and listname-request address localparts when the recipient_delimiter
       is set to "-".  This feature is useful for mailing lists.

parent_domain_matches_subdomains (default: see postconf -d output)

       A list of Postfix features where the pattern  "example.com"  also  matches  subdomains  of
       example.com,  instead  of  requiring  an explicit ".example.com" pattern.  This is planned
       backwards compatibility:   eventually,  all  Postfix  features  are  expected  to  require
       explicit ".example.com" style patterns when you really want to match subdomains.

       The following Postfix feature names are supported.

       Postfix version 1.0 and later
              debug_peer_list,    fast_flush_domains,    mynetworks,   permit_mx_backup_networks,
              relay_domains, transport_maps

       Postfix version 1.1 and later
              qmqpd_authorized_clients, smtpd_access_maps,

       Postfix version 2.8 and later
              postscreen_access_list

       Postfix version 3.0 and later
              smtpd_client_event_limit_exceptions

permit_mx_backup_networks (default: empty)

       Restrict the use of the permit_mx_backup SMTP access feature to only domains whose primary
       MX  hosts  match  the listed networks.  The parameter value syntax is the same as with the
       mynetworks parameter; note, however, that the default value is empty.

       Pattern  matching  of  domain  names  is  controlled  by  the  presence  or   absence   of
       "permit_mx_backup_networks" in the parent_domain_matches_subdomains parameter value.

pickup_service_name (default: pickup)

       The  name  of the pickup(8) service. This service picks up local mail submissions from the
       Postfix maildrop queue.

       This feature is available in Postfix 2.0 and later.

pipe_delivery_status_filter (default: $default_delivery_status_filter)

       Optional filter for the pipe(8) delivery agent to  change  the  delivery  status  code  or
       explanatory     text     of     successful     or     unsuccessful     deliveries.     See
       default_delivery_status_filter for details.

       This feature is available in Postfix 3.0 and later.

plaintext_reject_code (default: 450)

       The numerical Postfix SMTP server  response  code  when  a  request  is  rejected  by  the
       reject_plaintext_session restriction.

       This feature is available in Postfix 2.3 and later.

postmulti_control_commands (default: reload flush)

       The  postfix(1)  commands  that  the  postmulti(1)  instance  manager  treats as "control"
       commands, that operate on running instances. For these commands,  disabled  instances  are
       skipped.

       This feature is available in Postfix 2.6 and later.

postmulti_start_commands (default: start)

       The postfix(1) commands that the postmulti(1) instance manager treats as "start" commands.
       For these commands, disabled instances are "checked" rather than "started", and failure to
       "start" a member instance of an instance group will abort the start-up of later instances.

       This feature is available in Postfix 2.6 and later.

postmulti_stop_commands (default: see postconf -d output)

       The  postfix(1) commands that the postmulti(1) instance manager treats as "stop" commands.
       For these commands, disabled instances are skipped, and enabled instances are processed in
       reverse order.

       This feature is available in Postfix 2.6 and later.

postscreen_access_list (default: permit_mynetworks)

       Permanent  white/blacklist  for  remote  SMTP client IP addresses.  postscreen(8) searches
       this list  immediately  after  a  remote  SMTP  client  connects.   Specify  a  comma-  or
       whitespace-separated  list  of  commands  (in  upper  or lower case) or lookup tables. The
       search stops upon the first command that fires for the client IP address.

        permit_mynetworks
              Whitelist the client and terminate the search if  the  client  IP  address  matches
              $mynetworks.   Do  not  subject  the client to any before/after 220 greeting tests.
              Pass the connection immediately to a Postfix SMTP server process.
              Pattern matching of domain names is  controlled  by  the  presence  or  absence  of
              "postscreen_access_list" in the parent_domain_matches_subdomains parameter value.

        type:table
              Query  the  specified  lookup  table.  Each  table lookup result is an access list,
              except that access lists inside a table cannot specify type:table entries.
              To discourage the use of  hash,  btree,  etc.  tables,  there  is  no  support  for
              substring matching like smtpd(8). Use CIDR tables instead.

        permit
              Whitelist  the  client  and  terminate the search. Do not subject the client to any
              before/after 220 greeting tests. Pass the connection immediately to a Postfix  SMTP
              server process.

        reject
              Blacklist  the  client  and  terminate the search. Subject the client to the action
              configured with the postscreen_blacklist_action configuration parameter.

        dunno All postscreen(8) access lists implicitly have this command at the end.
              When  dunno is executed inside a lookup table, return from  the  lookup  table  and
              evaluate the next command.
              When   dunno  is executed outside a lookup table, terminate the search, and subject
              the client to the configured before/after 220 greeting tests.

       Example:

       /etc/postfix/main.cf:
           postscreen_access_list = permit_mynetworks,
                       cidr:/etc/postfix/postscreen_access.cidr
           postscreen_blacklist_action = enforce

       /etc/postfix/postscreen_access.cidr:
           # Rules are evaluated in the order as specified.
           # Blacklist 192.168.* except 192.168.0.1.
           192.168.0.1         dunno
           192.168.0.0/16      reject

       This feature is available in Postfix 2.8.

postscreen_bare_newline_action (default: ignore)

       The action that postscreen(8) takes when  a  remote  SMTP  client  sends  a  bare  newline
       character,  that  is,  a  newline  not  preceded  by  carriage return.  Specify one of the
       following:

       ignore Ignore the failure of this test. Allow other tests to complete.  Do not repeat this
              test  before  some  the result from some other test expires.  This option is useful
              for testing and collecting statistics without blocking mail permanently.

       enforce
              Allow other tests to complete. Reject attempts to deliver  mail  with  a  550  SMTP
              reply,  and  log  the helo/sender/recipient information.  Repeat this test the next
              time the client connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat this  test  the  next
              time the client connects.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_enable (default: no)

       Enable  "bare  newline"  SMTP  protocol tests in the postscreen(8) server. These tests are
       expensive: a remote SMTP client must disconnect after it passes the test,  before  it  can
       talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_ttl (default: 30d)

       The amount of time that postscreen(8) will use the result from a successful "bare newline"
       SMTP protocol test. During this time, the client IP address is excluded  from  this  test.
       The default is long because a remote SMTP client must disconnect after it passes the test,
       before it can talk to a real Postfix SMTP server.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time  unit).  Time units: s (seconds), m (minutes), h (hours), d (days), w
       (weeks).

       This feature is available in Postfix 2.8.

postscreen_blacklist_action (default: ignore)

       The action that postscreen(8) takes when a remote SMTP client is  permanently  blacklisted
       with the postscreen_access_list parameter.  Specify one of the following:

       ignore (default)
              Ignore  this result. Allow other tests to complete.  Repeat this test the next time
              the client connects.  This option is useful for testing and  collecting  statistics
              without blocking mail.

       enforce
              Allow  other  tests  to  complete.  Reject attempts to deliver mail with a 550 SMTP
              reply, and log the helo/sender/recipient information.  Repeat this  test  the  next
              time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat this test the next
              time the client connects.

       This feature is available in Postfix 2.8.

postscreen_cache_cleanup_interval (default: 12h)

       The amount of time between postscreen(8) cache cleanup runs.  Cache cleanup increases  the
       load  on  the  cache  database  and  should  therefore not be run frequently. This feature
       requires that the cache database supports the "delete" and "sequence" operators.   Specify
       a zero interval to disable cache cleanup.

       After  each  cache  cleanup  run, the postscreen(8) daemon logs the number of entries that
       were retained and dropped. A cleanup run is logged as "partial" when the daemon terminates
       early after "postfix reload", "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_cache_map (default: btree:$data_directory/postscreen_cache)

       Persistent storage for the postscreen(8) server decisions.

       To   share   a   postscreen(8)   cache   between  multiple  postscreen(8)  instances,  use
       "postscreen_cache_map = proxy:btree:/path/to/file".  This requires Postfix version 2.9  or
       later; earlier proxymap(8) implementations don't support cache cleanup. For an alternative
       approach see the memcache_table(5) manpage.

       This feature is available in Postfix 2.8.

postscreen_cache_retention_time (default: 7d)

       The amount of time that postscreen(8) will cache  an  expired  temporary  whitelist  entry
       before  it is removed. This prevents clients from being logged as "NEW" just because their
       cache entry expired an hour ago. It also prevents the cache from filling up  with  clients
       that passed some deep protocol test once and never came back.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_client_connection_count_limit (default: $smtpd_client_connection_count_limit)

       How  many  simultaneous  connections  any  remote  SMTP client is allowed to have with the
       postscreen(8) daemon. By default, this limit is the same as with the Postfix SMTP  server.
       Note  that  the  triage  process  can  take  several  seconds,  with  the  time  spent  in
       postscreen_greet_wait delay, and with the time spent talking to the postscreen(8) built-in
       dummy SMTP protocol engine.

       This feature is available in Postfix 2.8.

postscreen_command_count_limit (default: 20)

       The  limit  on  the total number of commands per SMTP session for postscreen(8)'s built-in
       SMTP protocol engine.  This SMTP engine defers or rejects all attempts  to  deliver  mail,
       therefore  there  is no need to enforce separate limits on the number of junk commands and
       error commands.

       This feature is available in Postfix 2.8.

postscreen_command_filter (default: $smtpd_command_filter)

       A mechanism to transform commands from remote SMTP clients.  See smtpd_command_filter  for
       further details.

       This feature is available in Postfix 2.8 and later.

postscreen_command_time_limit (default: normal: 300s, overload: 10s)

       The  time limit to read an entire command line with postscreen(8)'s built-in SMTP protocol
       engine.

       This feature is available in Postfix 2.8.

postscreen_disable_vrfy_command (default: $disable_vrfy_command)

       Disable the SMTP VRFY command in the postscreen(8) daemon.  See  disable_vrfy_command  for
       details.

       This feature is available in Postfix 2.8.

postscreen_discard_ehlo_keyword_address_maps (default: $smtpd_discard_ehlo_keyword_address_maps)

       Lookup  tables,  indexed by the remote SMTP client address, with case insensitive lists of
       EHLO keywords (pipelining, starttls, auth, etc.) that the postscreen(8)  server  will  not
       send  in  the  EHLO  response to a remote SMTP client. See smtpd_discard_ehlo_keywords for
       details.  The table is not searched by hostname for robustness reasons.

       This feature is available in Postfix 2.8 and later.

postscreen_discard_ehlo_keywords (default: $smtpd_discard_ehlo_keywords)

       A case insensitive list of EHLO keywords  (pipelining,  starttls,  auth,  etc.)  that  the
       postscreen(8)  server  will  not  send  in  the EHLO response to a remote SMTP client. See
       smtpd_discard_ehlo_keywords for details.

       This feature is available in Postfix 2.8 and later.

postscreen_dnsbl_action (default: ignore)

       The action that postscreen(8) takes when a remote SMTP client's combined  DNSBL  score  is
       equal  to  or  greater  than  a  threshold (as defined with the postscreen_dnsbl_sites and
       postscreen_dnsbl_threshold parameters).  Specify one of the following:

       ignore (default)
              Ignore the failure of this test. Allow other tests to complete.  Repeat  this  test
              the  next  time  the  client  connects.   This  option  is  useful  for testing and
              collecting statistics without blocking mail.

       enforce
              Allow other tests to complete. Reject attempts to deliver  mail  with  a  550  SMTP
              reply,  and  log  the helo/sender/recipient information.  Repeat this test the next
              time the client connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat this  test  the  next
              time the client connects.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_max_ttl (default: ${postscreen_dnsbl_ttl?{$postscreen_dnsbl_ttl}:{1}}h)

       The  maximum  amount  of  time  that  postscreen(8)  will use the result from a successful
       DNS-based reputation test before a client IP address is required to pass that test  again.
       If the DNS reply specifies a shorter TTL value, that value will be used unless it would be
       smaller than postscreen_dnsbl_min_ttl.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time  unit).  Time units: s (seconds), m (minutes), h (hours), d (days), w
       (weeks).

       This feature is available in Postfix 3.1. The default setting is backwards-compatible with
       older Postfix versions.

postscreen_dnsbl_min_ttl (default: 60s)

       The  minimum  amount  of  time  that  postscreen(8)  will use the result from a successful
       DNS-based reputation test before a client IP address is required to pass that test  again.
       If  the DNS reply specifies a larger TTL value, that value will be used unless it would be
       larger than postscreen_dnsbl_max_ttl.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time  unit).  Time units: s (seconds), m (minutes), h (hours), d (days), w
       (weeks).

       This feature is available in Postfix 3.1.

postscreen_dnsbl_reply_map (default: empty)

       A mapping from actual DNSBL domain name which includes a secret  password,  to  the  DNSBL
       domain  name  that  postscreen  will  reply with when it rejects mail.  When no mapping is
       found, the actual DNSBL domain will be used.

       For maximal stability it is best to use a file that is read into  memory  such  as  pcre:,
       regexp:  or  texthash:  (texthash:  is similar to hash:, except a) there is no need to run
       postmap(1) before the file can be used, and b) texthash: does not detect changes after the
       file is read).

       Example:

       /etc/postfix/main.cf:
           postscreen_dnsbl_reply_map = texthash:/etc/postfix/dnsbl_reply

       /etc/postfix/dnsbl_reply:
          secret.zen.spamhaus.org      zen.spamhaus.org

       This feature is available in Postfix 2.8.

postscreen_dnsbl_sites (default: empty)

       Optional list of DNS white/blacklist domains, filters and weight factors. When the list is
       non-empty, the dnsblog(8) daemon will query these domains with the IP addresses of  remote
       SMTP  clients,  and  postscreen(8)  will  update  an  SMTP  client's DNSBL score with each
       non-error reply.

       Caution: when postscreen rejects mail, it replies with the  DNSBL  domain  name.  Use  the
       postscreen_dnsbl_reply_map feature to hide "password" information in DNSBL domain names.

       When  a  client's  score  is  equal  to  or  greater  than  the  threshold  specified with
       postscreen_dnsbl_threshold, postscreen(8) can drop the connection  with  the  remote  SMTP
       client.

       Specify a list of domain=filter*weight entries, separated by comma or whitespace.

       ·      When  no  "=filter" is specified, postscreen(8) will use any non-error DNSBL reply.
              Otherwise, postscreen(8) uses only DNSBL replies that match the filter. The  filter
              has  the  form  d.d.d.d,  where  each  d  is  a number, or a pattern inside [] that
              contains one or more ";"-separated numbers or number..number ranges.

       ·      When no "*weight" is specified, postscreen(8) increments the remote  SMTP  client's
              DNSBL  score  by  1.   Otherwise,  the  weight  must  be  an  integral  number, and
              postscreen(8) adds the specified weight to the remote SMTP  client's  DNSBL  score.
              Specify a negative number for whitelisting.

       ·      When   one   postscreen_dnsbl_sites   entry   produces  multiple  DNSBL  responses,
              postscreen(8) applies the weight at most once.

       Examples:

       To use example.com as a high-confidence blocklist, and to block mail with example.net  and
       example.org only when both agree:

       postscreen_dnsbl_threshold = 2
       postscreen_dnsbl_sites = example.com*2, example.net, example.org

       To filter only DNSBL replies containing 127.0.0.4:

       postscreen_dnsbl_sites = example.com=127.0.0.4

       This feature is available in Postfix 2.8.

postscreen_dnsbl_threshold (default: 1)

       The  inclusive  lower bound for blocking a remote SMTP client, based on its combined DNSBL
       score as defined with the postscreen_dnsbl_sites parameter.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_timeout (default: 10s)

       The time limit for DNSBL or DNSWL lookups. This is  separate  from  the  timeouts  in  the
       dnsblog(8) daemon which are defined by system resolver(3) routines.

       This feature is available in Postfix 3.0.

postscreen_dnsbl_ttl (default: 1h)

       The  amount  of  time  that  postscreen(8) will use the result from a successful DNS-based
       reputation test before a client IP address is required to pass that test again.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time  unit).  Time units: s (seconds), m (minutes), h (hours), d (days), w
       (weeks).

       This feature is available in Postfix 2.8-3.0. It was replaced by  postscreen_dnsbl_max_ttl
       in Postfix 3.1.

postscreen_dnsbl_whitelist_threshold (default: 0)

       Allow a remote SMTP client to skip "before" and "after 220 greeting" protocol tests, based
       on its combined DNSBL score as defined with the postscreen_dnsbl_sites parameter.

       Specify  a  negative  value  to  enable  this  feature.   When   a   client   passes   the
       postscreen_dnsbl_whitelist_threshold  without  having  failed  other tests, all pending or
       disabled  tests  are  flagged  as  completed  with   a   time-to-live   value   equal   to
       postscreen_dnsbl_ttl.   When  a  test  was  already  completed,  its time-to-live value is
       updated if it was less than postscreen_dnsbl_ttl.

       This feature is available in Postfix 2.11.

postscreen_enforce_tls (default: $smtpd_enforce_tls)

       Mandatory TLS: announce STARTTLS support to remote SMTP clients, and require that  clients
       use TLS encryption.  See smtpd_postscreen_enforce_tls for details.

       This    feature    is   available   in   Postfix   2.8   and   later.    Preferably,   use
       postscreen_tls_security_level instead.

postscreen_expansion_filter (default: see postconf -d output)

       List of characters that are permitted in  postscreen_reject_footer  attribute  expansions.
       See smtpd_expansion_filter for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_forbidden_commands (default: $smtpd_forbidden_commands)

       List  of  commands  that  the  postscreen(8)  server  considers  in  violation of the SMTP
       protocol. See smtpd_forbidden_commands for syntax, and  postscreen_non_smtp_command_action
       for possible actions.

       This feature is available in Postfix 2.8.

postscreen_greet_action (default: ignore)

       The  action  that  postscreen(8)  takes  when  a remote SMTP client speaks before its turn
       within the time specified with the postscreen_greet_wait parameter.  Specify  one  of  the
       following:

       ignore (default)
              Ignore  the  failure of this test. Allow other tests to complete.  Repeat this test
              the next time  the  client  connects.   This  option  is  useful  for  testing  and
              collecting statistics without blocking mail.

       enforce
              Allow  other  tests  to  complete.  Reject attempts to deliver mail with a 550 SMTP
              reply, and log the helo/sender/recipient information.  Repeat this  test  the  next
              time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat this test the next
              time the client connects.

       In either case, postscreen(8) will not whitelist the remote SMTP client IP address.

       This feature is available in Postfix 2.8.

postscreen_greet_banner (default: $smtpd_banner)

       The text in the optional "220-text..." server response that postscreen(8) sends  ahead  of
       the  real  Postfix SMTP server's "220 text..." response, in an attempt to confuse bad SMTP
       clients so that they speak before their turn  (pre-greet).   Specify  an  empty  value  to
       disable this feature.

       This feature is available in Postfix 2.8.

postscreen_greet_ttl (default: 1d)

       The amount of time that postscreen(8) will use the result from a successful PREGREET test.
       During this time, the client IP address  is  excluded  from  this  test.  The  default  is
       relatively  short,  because  a  good  client  can  immediately talk to a real Postfix SMTP
       server.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time  unit).  Time units: s (seconds), m (minutes), h (hours), d (days), w
       (weeks).

       This feature is available in Postfix 2.8.

postscreen_greet_wait (default: normal: 6s, overload: 2s)

       The amount of time that postscreen(8) will wait for an  SMTP  client  to  send  a  command
       before  its turn, and for DNS blocklist lookup results to arrive (default: up to 2 seconds
       under stress, up to 6 seconds otherwise).

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_helo_required (default: $smtpd_helo_required)

       Require that a remote SMTP client sends HELO or EHLO before commencing a MAIL transaction.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_action (default: drop)

       The  action  that postscreen(8) takes when a remote SMTP client sends non-SMTP commands as
       specified with the postscreen_forbidden_commands parameter.  Specify one of the following:

       ignore Ignore the failure of this test. Allow other tests to complete.  Do not repeat this
              test  before  some  the result from some other test expires.  This option is useful
              for testing and collecting statistics without blocking mail permanently.

       enforce
              Allow other tests to complete. Reject attempts to deliver  mail  with  a  550  SMTP
              reply,  and  log  the helo/sender/recipient information.  Repeat this test the next
              time the client connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat this  test  the  next
              time the client connects. This action is the same as with the Postfix SMTP server's
              smtpd_forbidden_commands feature.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_enable (default: no)

       Enable "non-SMTP command" tests in the postscreen(8) server. These tests are expensive:  a
       client must disconnect after it passes the test, before it can talk to a real Postfix SMTP
       server.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_ttl (default: 30d)

       The  amount  of  time  that  postscreen(8)  will  use  the  result   from   a   successful
       "non_smtp_command" SMTP protocol test. During this time, the client IP address is excluded
       from this test. The default is long because a client must disconnect after it  passes  the
       test, before it can talk to a real Postfix SMTP server.

       Specify  a  non-zero time value (an integral value plus an optional one-letter suffix that
       specifies the time unit).  Time units: s (seconds), m (minutes), h (hours),  d  (days),  w
       (weeks).

       This feature is available in Postfix 2.8.

postscreen_pipelining_action (default: enforce)

       The  action  that  postscreen(8)  takes  when a remote SMTP client sends multiple commands
       instead of sending one command and waiting for the server to respond.  Specify one of  the
       following:

       ignore Ignore the failure of this test. Allow other tests to complete.  Do not repeat this
              test before some the result from some other test expires.  This  option  is  useful
              for testing and collecting statistics without blocking mail permanently.

       enforce
              Allow  other  tests  to  complete.  Reject attempts to deliver mail with a 550 SMTP
              reply, and log the helo/sender/recipient information.  Repeat this  test  the  next
              time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat this test the next
              time the client connects.

       This feature is available in Postfix 2.8.

postscreen_pipelining_enable (default: no)

       Enable "pipelining" SMTP protocol tests in  the  postscreen(8)  server.  These  tests  are
       expensive: a good client must disconnect after it passes the test, before it can talk to a
       real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_pipelining_ttl (default: 30d)

       The amount of time that postscreen(8) will use the result from a  successful  "pipelining"
       SMTP  protocol  test.  During this time, the client IP address is excluded from this test.
       The default is long because a good client must disconnect after it passes the test, before
       it can talk to a real Postfix SMTP server.

       Specify  a  non-zero time value (an integral value plus an optional one-letter suffix that
       specifies the time unit).  Time units: s (seconds), m (minutes), h (hours),  d  (days),  w
       (weeks).

       This feature is available in Postfix 2.8.

postscreen_post_queue_limit (default: $default_process_limit)

       The  number  of  clients  that  can be waiting for service from a real Postfix SMTP server
       process. When this queue is full, all clients will receive a 421 response.

       This feature is available in Postfix 2.8.

postscreen_pre_queue_limit (default: $default_process_limit)

       The number of non-whitelisted clients that can be waiting for a decision whether they will
       receive  service  from  a  real  Postfix SMTP server process. When this queue is full, all
       non-whitelisted clients will receive a 421 response.

       This feature is available in Postfix 2.8.

postscreen_reject_footer (default: $smtpd_reject_footer)

       Optional information that is appended after a 4XX or 5XX  postscreen(8)  server  response.
       See smtpd_reject_footer for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_tls_security_level (default: $smtpd_tls_security_level)

       The  SMTP  TLS  security  level  for  the  postscreen(8) server; when a non-empty value is
       specified,   this   overrides   the    obsolete    parameters    postscreen_use_tls    and
       postscreen_enforce_tls. See smtpd_tls_security_level for details.

       This feature is available in Postfix 2.8 and later.

postscreen_upstream_proxy_protocol (default: empty)

       The  name  of the proxy protocol used by an optional before-postscreen proxy agent. When a
       proxy agent is used, this protocol conveys local and remote address and port  information.
       Specify "postscreen_upstream_proxy_protocol = haproxy" to enable the haproxy protocol.

       This feature is available in Postfix 2.10 and later.

postscreen_upstream_proxy_timeout (default: 5s)

       The     time     limit     for     the     proxy     protocol     specified    with    the
       postscreen_upstream_proxy_protocol parameter.

       This feature is available in Postfix 2.10 and later.

postscreen_use_tls (default: $smtpd_use_tls)

       Opportunistic TLS: announce STARTTLS support to remote SMTP clients, but  do  not  require
       that clients use TLS encryption.

       This    feature    is   available   in   Postfix   2.8   and   later.    Preferably,   use
       postscreen_tls_security_level instead.

postscreen_watchdog_timeout (default: 10s)

       How much time a postscreen(8) process may take to respond to a remote SMTP client  command
       or  to  perform  a  cache  operation before it is terminated by a built-in watchdog timer.
       This is a safety mechanism that prevents postscreen(8) from becoming non-responsive due to
       a  bug  in  Postfix  itself  or in system software.  To avoid false alarms and unnecessary
       cache corruption this limit cannot be set under 10s.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time  unit).  Time units: s (seconds), m (minutes), h (hours), d (days), w
       (weeks).

       This feature is available in Postfix 2.8.

postscreen_whitelist_interfaces (default: static:all)

       A list of local postscreen(8) server IP addresses  where  a  non-whitelisted  remote  SMTP
       client  can  obtain  postscreen(8)'s  temporary  whitelist status. This status is required
       before the client can talk to a Postfix SMTP server process.  By  default,  a  client  can
       obtain postscreen(8)'s whitelist status on any local postscreen(8) server IP address.

       When   postscreen(8)   listens   on   both   primary   and   backup   MX   addresses,  the
       postscreen_whitelist_interfaces  parameter  can  be  configured  to  give  the   temporary
       whitelist  status  only  when  a client connects to a primary MX address. Once a client is
       whitelisted it can talk to a Postfix SMTP  server  on  any  address.  Thus,  clients  that
       connect  only  to  backup  MX  addresses  will never become whitelisted, and will never be
       allowed to talk to a Postfix SMTP server process.

       Specify a list of network addresses  or  network/netmask  patterns,  separated  by  commas
       and/or  whitespace. The netmask specifies the number of bits in the network part of a host
       address. Continue long lines by starting the next line with whitespace.

       You can also specify "/file/name" or "type:table" patterns.   A  "/file/name"  pattern  is
       replaced  by  its  contents;  a  "type:table"  lookup  table is matched when a table entry
       matches a lookup string (the lookup result is ignored).

       The list is matched left to right, and the  search  stops  on  the  first  match.  Specify
       "!pattern" to exclude an address or network block from the list.

       Note:   IP   version   6   address   information  must  be  specified  inside  []  in  the
       postscreen_whitelist_interfaces value, and  in  files  specified  with  "/file/name".   IP
       version  6  addresses  contain  the  ":" character, and would otherwise be confused with a
       "type:table" pattern.

       Example:

       /etc/postfix/main.cf:
           # Don't whitelist connections to the backup IP address.
           postscreen_whitelist_interfaces = !168.100.189.8, static:all

       This feature is available in Postfix 2.9 and later.

prepend_delivered_header (default: command, file, forward)

       The message delivery contexts  where  the  Postfix  local(8)  delivery  agent  prepends  a
       Delivered-To:   message  header  with  the  address  that  the mail was delivered to. This
       information is used for mail delivery loop detection.

       By default, the  Postfix  local  delivery  agent  prepends  a  Delivered-To:  header  when
       forwarding  mail  and  when  delivering  to  file  (mailbox)  and command. Turning off the
       Delivered-To: header when forwarding mail is not recommended.

       Specify zero or more of forward, file, or command.

       Example:

       prepend_delivered_header = forward

process_id (read-only)

       The process ID of a Postfix command or daemon process.

process_id_directory (default: pid)

       The location of Postfix PID files relative  to  $queue_directory.   This  is  a  read-only
       parameter.

process_name (read-only)

       The process name of a Postfix command or daemon process.

propagate_unmatched_extensions (default: canonical, virtual)

       What  address  lookup  tables  copy an address extension from the lookup key to the lookup
       result.

       For example, with a virtual(5) mapping of "joe@example.com =>  joe.user@example.net",  the
       address "joe+foo@example.com" would rewrite to "joe.user+foo@example.net".

       Specify  zero  or  more  of  canonical, virtual, alias, forward, include or generic. These
       cause address extension propagation with canonical(5), virtual(5),  and  aliases(5)  maps,
       with  local(8)  .forward  and  :include:  file  lookups,  and  with  smtp(8) generic maps,
       respectively.

       Note: enabling this feature for types other than canonical and virtual is likely to  cause
       problems  when  mail  is  forwarded to other sites, especially with mail that is sent to a
       mailing list exploder address.

       Examples:

       propagate_unmatched_extensions = canonical, virtual, alias,
               forward, include
       propagate_unmatched_extensions = canonical, virtual

proxy_interfaces (default: empty)

       The network interface addresses that this mail system receives mail on by way of  a  proxy
       or network address translation unit.

       This feature is available in Postfix 2.0 and later.

       You  must  specify your "outside" proxy/NAT addresses when your system is a backup MX host
       for other domains, otherwise mail delivery loops will happen when the primary MX  host  is
       down.

       Example:

       proxy_interfaces = 1.2.3.4

proxy_read_maps (default: see postconf -d output)

       The  lookup  tables  that  the  proxymap(8)  server is allowed to access for the read-only
       service.

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.   Table
       references that don't begin with proxy: are ignored.

       This feature is available in Postfix 2.0 and later.

proxy_write_maps (default: see postconf -d output)

       The  lookup  tables  that  the  proxymap(8) server is allowed to access for the read-write
       service. Postfix-owned local database files  should  be  stored  under  the  Postfix-owned
       data_directory.  Table references that don't begin with proxy: are ignored.

       This feature is available in Postfix 2.5 and later.

proxymap_service_name (default: proxymap)

       The  name  of  the  proxymap  read-only  table  lookup  service.  This service is normally
       implemented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

proxywrite_service_name (default: proxywrite)

       The name of the proxywrite read-write table lookup  service.   This  service  is  normally
       implemented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

qmgr_clog_warn_time (default: 300s)

       The  minimal delay between warnings that a specific destination is clogging up the Postfix
       active queue. Specify 0 to disable.

       This feature is enabled with the helpful_warnings parameter.

       This feature is available in Postfix 2.0 and later.

qmgr_daemon_timeout (default: 1000s)

       How much time a Postfix queue manager process may take to handle a request  before  it  is
       terminated by a built-in watchdog timer.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

       This feature is available in Postfix 2.8 and later.

qmgr_fudge_factor (default: 100)

       Obsolete feature: the percentage of delivery resources that a busy mail system will use up
       for delivery of a large mailing  list message.

       This  feature  exists  only  in  the oqmgr(8) old queue manager. The current queue manager
       solves the problem in a better way.

qmgr_ipc_timeout (default: 60s)

       The time limit for the queue manager to send  or  receive  information  over  an  internal
       communication  channel.   The  purpose is to break out of deadlock situations. If the time
       limit is exceeded the software either retries or aborts the operation.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

       This feature is available in Postfix 2.8 and later.

qmgr_message_active_limit (default: 20000)

       The maximal number of messages in the active queue.

qmgr_message_recipient_limit (default: 20000)

       The  maximal  number  of  recipients  held in memory by the Postfix queue manager, and the
       maximal size of the short-term, in-memory "dead" destination status cache.

qmgr_message_recipient_minimum (default: 10)

       The minimal number of in-memory recipients for any message. This takes priority  over  any
       other  in-memory  recipient  limits (i.e., the global qmgr_message_recipient_limit and the
       per transport _recipient_limit) if necessary. The minimum value allowed for this parameter
       is 1.

qmqpd_authorized_clients (default: empty)

       What remote QMQP clients are allowed to connect to the Postfix QMQP server port.

       By  default, no client is allowed to use the service. This is because the QMQP server will
       relay mail to any destination.

       Specify a list of client patterns. A list pattern specifies a host name, a domain name, an
       internet  address,  or a network/mask pattern, where the mask specifies the number of bits
       in the network part.  When a pattern specifies a file name, its contents  are  substituted
       for  the  file name; when a pattern is a "type:table" table specification, table lookup is
       used instead.

       Patterns are separated by whitespace and/or  commas.  In  order  to  reverse  the  result,
       precede  a pattern with an exclamation point (!). The form "!/file/name" is supported only
       in Postfix version 2.4 and later.

       Pattern  matching  of  domain  names  is  controlled  by  the  presence  or   absence   of
       "qmqpd_authorized_clients" in the parent_domain_matches_subdomains parameter value.

       Example:

       qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24

qmqpd_client_port_logging (default: no)

       Enable  logging of the remote QMQP client port in addition to the hostname and IP address.
       The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

qmqpd_error_delay (default: 1s)

       How long the Postfix QMQP server will pause before sending a negative reply to the  remote
       QMQP client. The purpose is to slow down confused or malicious clients.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

qmqpd_timeout (default: 300s)

       The time limit for sending or receiving information over the network.  If a read or  write
       operation blocks for more than $qmqpd_timeout seconds the Postfix QMQP server gives up and
       disconnects.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

queue_directory (default: see postconf -d output)

       The  location  of  the  Postfix  top-level  queue directory. This is the root directory of
       Postfix daemon processes that run chrooted.

queue_file_attribute_count_limit (default: 100)

       The maximal number of (name=value) attributes that may be stored in a Postfix queue  file.
       The limit is enforced by the cleanup(8) server.

       This feature is available in Postfix 2.0 and later.

queue_minfree (default: 0)

       The  minimal  amount  of  free  space  in bytes in the queue file system that is needed to
       receive mail.  This is currently used by the Postfix SMTP server  to  decide  if  it  will
       accept any mail at all.

       By  default,  the  Postfix  SMTP server rejects MAIL FROM commands when the amount of free
       space is less than 1.5*$message_size_limit (Postfix version 2.1 and later).  To specify  a
       higher  minimum  free  space  limit,  specify  a  queue_minfree  value  that  is  at least
       1.5*$message_size_limit.

       With Postfix versions 2.0 and earlier, a queue_minfree value of zero  means  there  is  no
       minimum required amount of free space.

queue_run_delay (default: 300s)

       The  time  between  deferred  queue  scans  by the queue manager; prior to Postfix 2.4 the
       default value was 1000s.

       This parameter should be set  less  than  or  equal  to  $minimal_backoff_time.  See  also
       $maximal_backoff_time.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

queue_service_name (default: qmgr)

       The name of the qmgr(8) service. This service manages  the  Postfix  queue  and  schedules
       delivery requests.

       This feature is available in Postfix 2.0 and later.

rbl_reply_maps (default: empty)

       Optional  lookup  tables  with  RBL  response templates. The tables are indexed by the RBL
       domain name. By  default,  Postfix  uses  the  default  template  as  specified  with  the
       default_rbl_reply configuration parameter. See there for a discussion of the syntax of RBL
       reply templates.

       This feature is available in Postfix 2.0 and later.

readme_directory (default: see postconf -d output)

       The location of Postfix README files that describe how to build, configure  or  operate  a
       specific Postfix subsystem or feature.

receive_override_options (default: empty)

       Enable  or  disable  recipient validation, built-in content filtering, or address mapping.
       Typically, these are specified in master.cf as command-line arguments  for  the  smtpd(8),
       qmqpd(8) or pickup(8) daemons.

       Specify  zero or more of the following options.  The options override main.cf settings and
       are either implemented by  smtpd(8),  qmqpd(8),  or  pickup(8)  themselves,  or  they  are
       forwarded to the cleanup server.

       no_unknown_recipient_checks
              Do  not  try  to  reject  unknown recipients (SMTP server only).  This is typically
              specified AFTER an external content filter.

       no_address_mappings
              Disable  canonical  address  mapping,  virtual   alias   map   expansion,   address
              masquerading,  and  automatic BCC (blind carbon-copy) recipients. This is typically
              specified BEFORE an external content filter.

       no_header_body_checks
              Disable header/body_checks. This is typically specified AFTER an  external  content
              filter.

       no_milters
              Disable  Milter  (mail  filter)  applications. This is typically specified AFTER an
              external content filter.

       Note: when the "BEFORE content filter" receive_override_options setting  is  specified  in
       the  main.cf  file, specify the "AFTER content filter" receive_override_options setting in
       master.cf (and vice versa).

       Examples:

       receive_override_options =
           no_unknown_recipient_checks, no_header_body_checks
       receive_override_options = no_address_mappings

       This feature is available in Postfix 2.1 and later.

recipient_bcc_maps (default: empty)

       Optional BCC (blind carbon-copy) address lookup tables, indexed by recipient address.  The
       BCC address (multiple results are not supported) is added when mail enters from outside of
       Postfix.

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.  Tables
       will be searched in the specified order until a match is found.

       The table search order is as follows:

       ·      Look  up  the  "user+extension@domain.tld"  address  including the optional address
              extension.

       ·      Look up the "user@domain.tld" address without the optional address extension.

       ·      Look up the "user+extension" address local part when the  recipient  domain  equals
              $myorigin, $mydestination, $inet_interfaces or $proxy_interfaces.

       ·      Look  up  the "user" address local part when the recipient domain equals $myorigin,
              $mydestination, $inet_interfaces or $proxy_interfaces.

       ·      Look up the "@domain.tld" part.

       Note: with Postfix 2.3 and later the BCC address is added as  if  it  was  specified  with
       NOTIFY=NONE.  The  sender  will  not be notified when the BCC address is undeliverable, as
       long as all down-stream software implements RFC 3461.

       Note: with Postfix 2.2 and earlier the sender will unconditionally be  notified  when  the
       BCC address is undeliverable.

       Note:  automatic  BCC  recipients  are produced only for new mail.  To avoid mailer loops,
       automatic BCC recipients are not generated after  Postfix  forwards  mail  internally,  or
       after Postfix generates mail itself.

       Example:

       recipient_bcc_maps = hash:/etc/postfix/recipient_bcc

       After a change, run "postmap /etc/postfix/recipient_bcc".

       This feature is available in Postfix 2.1 and later.

recipient_canonical_classes (default: envelope_recipient, header_recipient)

       What  addresses  are  subject  to  recipient_canonical_maps  address mapping.  By default,
       recipient_canonical_maps address mapping is applied to envelope recipient  addresses,  and
       to header recipient addresses.

       Specify one or more of: envelope_recipient, header_recipient

       This feature is available in Postfix 2.2 and later.

recipient_canonical_maps (default: empty)

       Optional  address  mapping lookup tables for envelope and header recipient addresses.  The
       table format and lookups are documented in canonical(5).

       Note: $recipient_canonical_maps is processed before $canonical_maps.

       Example:

       recipient_canonical_maps = hash:/etc/postfix/recipient_canonical

recipient_delimiter (default: empty)

       The set of characters  that  can  separate  a  user  name  from  its  extension  (example:
       user+foo), or a .forward file name from its extension (example: .forward+foo).  Basically,
       the software tries user+foo and  .forward+foo  before  trying  user  and  .forward.   This
       implementation  recognizes  one delimiter character and one extension per email address or
       .forward file name.

       When the recipient_delimiter set contains multiple characters (Postfix 2.11 and later),  a
       user  name  or  .forward  file name is separated from its extension by the first character
       that matches the recipient_delimiter set.

       See  canonical(5),  local(8),   relocated(5)   and   virtual(5)   for   the   effects   of
       recipient_delimiter on lookups in aliases, canonical, virtual, and relocated maps, and see
       the propagate_unmatched_extensions parameter for propagating an extension from  one  email
       address to another.

       When     used    in    command_execution_directory,    forward_path,    or    luser_relay,
       ${recipient_delimiter} is replaced with the actual recipient delimiter that was  found  in
       the  recipient  email address (Postfix 2.11 and later), or it is replaced with the main.cf
       recipient_delimiter parameter value (Postfix 2.10 and earlier).

       The recipient_delimiter is not  applied  to  the  mailer-daemon  address,  the  postmaster
       address,  or  the  double-bounce  address.  With the default "owner_request_special = yes"
       setting, the recipient_delimiter is  also  not  applied  to  addresses  with  the  special
       "owner-" prefix or the special "-request" suffix.

       Examples:

       # Handle Postfix-style extensions.
       recipient_delimiter = +

       # Handle both Postfix and qmail extensions (Postfix 2.11 and later).
       recipient_delimiter = +-

       # Use .forward for mail without address extension, and for mail with
       # an unrecognized address extension.
       forward_path = $home/.forward${recipient_delimiter}${extension},
           $home/.forward

reject_code (default: 554)

       The  numerical  Postfix  SMTP  server  response  code when a remote SMTP client request is
       rejected by the "reject" restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

reject_tempfail_action (default: defer_if_permit)

       The Postfix SMTP server's action when a reject-type restriction fails due to  a  temporary
       error condition. Specify "defer" to defer the remote SMTP client request immediately. With
       the default "defer_if_permit" action, the  Postfix  SMTP  server  continues  to  look  for
       opportunities  to reject mail, and defers the client request only if it would otherwise be
       accepted.

       For        finer        control,        see:         unverified_recipient_tempfail_action,
       unverified_sender_tempfail_action,           unknown_address_tempfail_action,          and
       unknown_helo_hostname_tempfail_action.

       This feature is available in Postfix 2.6 and later.

relay_clientcerts (default: empty)

       List of tables with remote SMTP client-certificate fingerprints or public key fingerprints
       (Postfix  2.9  and  later)  for  which  the Postfix SMTP server will allow access with the
       permit_tls_clientcerts feature.  The fingerprint digest algorithm is configurable via  the
       smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to Postfix version 2.5).

       Postfix  lookup tables are in the form of (key, value) pairs.  Since we only need the key,
       the  value  can  be   chosen   freely,   e.g.    the   name   of   the   user   or   host:
       D7:04:2F:A7:0B:8C:A5:21:FA:31:77:E1:41:8A:EE:80 lutzpc.at.home

       Example:

       relay_clientcerts = hash:/etc/postfix/relay_clientcerts

       For  more  fine-grained control, use check_ccert_access to select an appropriate access(5)
       policy for each client.  See RESTRICTION_CLASS_README.

       Note: Postfix  2.9.0-2.9.5  computed  the  public  key  fingerprint  incorrectly.  To  use
       public-key fingerprints, upgrade to Postfix 2.9.6 or later.

       This feature is available with Postfix version 2.2.

relay_destination_concurrency_limit (default: $default_destination_concurrency_limit)

       The  maximal  number  of parallel deliveries to the same destination via the relay message
       delivery transport. This limit is enforced by the  queue  manager.  The  message  delivery
       transport name is the first field in the entry in the master.cf file.

       This feature is available in Postfix 2.0 and later.

relay_destination_recipient_limit (default: $default_destination_recipient_limit)

       The  maximal  number  of  recipients per message for the relay message delivery transport.
       This limit is enforced by the queue manager. The message delivery transport  name  is  the
       first field in the entry in the master.cf file.

       Setting    this    parameter    to    a    value    of    1   changes   the   meaning   of
       relay_destination_concurrency_limit from  concurrency  per  domain  into  concurrency  per
       recipient.

       This feature is available in Postfix 2.0 and later.

relay_domains (default: Postfix >= 3.0: empty, Postfix < 3.0: $mydestination)

       What  destination  domains  (and  subdomains  thereof) this system will relay mail to. For
       details  about  how  the  relay_domains  value  is  used,  see  the  description  of   the
       permit_auth_destination and reject_unauth_destination SMTP recipient restrictions.

       Domains  that  match  $relay_domains are delivered with the $relay_transport mail delivery
       transport. The SMTP server validates recipient addresses  with  $relay_recipient_maps  and
       rejects  non-existent  recipients.  See  also  the  relay  domains  address  class  in the
       ADDRESS_CLASS_README file.

       Note: Postfix will not automatically forward mail for domains that  list  this  system  as
       their  primary  or backup MX host. See the permit_mx_backup restriction in the postconf(5)
       manual page.

       Specify a list of host or domain  names,  "/file/name"  patterns  or  "type:table"  lookup
       tables,  separated  by commas and/or whitespace.  Continue long lines by starting the next
       line with whitespace. A "/file/name" pattern is replaced by its contents;  a  "type:table"
       lookup  table  is matched when a (parent) domain appears as lookup key. Specify "!pattern"
       to exclude a domain from the list. The form "!/file/name" is  supported  only  in  Postfix
       version 2.4 and later.

       Pattern   matching   of  domain  names  is  controlled  by  the  presence  or  absence  of
       "relay_domains" in the parent_domain_matches_subdomains parameter value.

relay_domains_reject_code (default: 554)

       The numerical Postfix SMTP server response code when a client request is rejected  by  the
       reject_unauth_destination recipient restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

relay_recipient_maps (default: empty)

       Optional  lookup tables with all valid addresses in the domains that match $relay_domains.
       Specify @domain as a wild-card for domains that have no valid recipient list, and become a
       source  of  backscatter  mail:  Postfix  accepts spam for non-existent recipients and then
       floods  innocent  people  with  undeliverable  mail.   Technically,  tables  listed   with
       $relay_recipient_maps  are used as lists: Postfix needs to know only if a lookup string is
       found or not, but it does not use the result from table lookup.

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.  Tables
       will be searched in the specified order until a match is found.

       If  this  parameter is non-empty, then the Postfix SMTP server will reject mail to unknown
       relay users. This feature is off by default.

       See also the relay domains address class in the ADDRESS_CLASS_README file.

       Example:

       relay_recipient_maps = hash:/etc/postfix/relay_recipients

       This feature is available in Postfix 2.0 and later.

relay_transport (default: relay)

       The default mail delivery transport  and  next-hop  destination  for  remote  delivery  to
       domains  listed  with  $relay_domains.  In  order  of  decreasing  precedence, the nexthop
       destination is taken from $relay_transport, $sender_dependent_relayhost_maps,  $relayhost,
       or  from  the  recipient  domain.  This information can be overruled with the transport(5)
       table.

       Specify a string of the form transport:nexthop, where transport is  the  name  of  a  mail
       delivery transport defined in master.cf.  The :nexthop destination is optional; its syntax
       is documented in the manual page of the corresponding delivery agent.

       See also the relay domains address class in the ADDRESS_CLASS_README file.

       This feature is available in Postfix 2.0 and later.

relayhost (default: empty)

       The next-hop destination of non-local  mail;  overrides  non-local  domains  in  recipient
       addresses.      This      information      is      overruled     with     relay_transport,
       sender_dependent_default_transport_maps,                                default_transport,
       sender_dependent_relayhost_maps and with the transport(5) table.

       On  an  intranet,  specify the organizational domain name. If your internal DNS uses no MX
       records, specify the name of the intranet gateway host instead.

       In the case of SMTP, specify a  domain  name,  hostname,  hostname:port,  [hostname]:port,
       [hostaddress] or [hostaddress]:port. The form [hostname] turns off MX lookups.

       If you're connected via UUCP, see the UUCP_README file for useful information.

       Examples:

       relayhost = $mydomain
       relayhost = [gateway.example.com]
       relayhost = uucphost
       relayhost = [an.ip.add.ress]

relocated_maps (default: empty)

       Optional  lookup  tables  with new contact information for users or domains that no longer
       exist.  The table format and lookups are documented in relocated(5).

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.  Tables
       will be searched in the specified order until a match is found.

       If  you  use this feature, run "postmap /etc/postfix/relocated" to build the necessary DBM
       or DB file after change, then "postfix reload" to make the changes visible.

       Examples:

       relocated_maps = dbm:/etc/postfix/relocated
       relocated_maps = hash:/etc/postfix/relocated

remote_header_rewrite_domain (default: empty)

       Don't rewrite message headers from remote clients at all when  this  parameter  is  empty;
       otherwise,  rewrite  message  headers  and  append the specified domain name to incomplete
       addresses.  The  local_header_rewrite_clients  parameter  controls  what  clients  Postfix
       considers local.

       Examples:

       The  safe setting: append "domain.invalid" to incomplete header addresses from remote SMTP
       clients, so that those addresses cannot be confused with local addresses.

           remote_header_rewrite_domain = domain.invalid

       The default, purist, setting: don't rewrite headers from remote clients at all.

           remote_header_rewrite_domain =

require_home_directory (default: no)

       Require that a  local(8)  recipient's  home  directory  exists  before  mail  delivery  is
       attempted.  By  default  this  test  is  disabled.  It can be useful for environments that
       import  home  directories  to  the  mail  server  (IMPORTING  HOME  DIRECTORIES   IS   NOT
       RECOMMENDED).

reset_owner_alias (default: no)

       Reset  the  local(8)  delivery  agent's idea of the owner-alias attribute, when delivering
       mail to a child alias that does not have its own owner alias.

       This feature is available in Postfix 2.8 and  later.  With  older  Postfix  releases,  the
       behavior is as if this parameter is set to "yes".

       As  documented  in  aliases(5), when an alias name has a companion alias named owner-name,
       this will replace the envelope sender address, so that delivery errors will be reported to
       the  owner  alias  instead  of  the  sender. This configuration is recommended for mailing
       lists.

       A less known property of the owner alias is that it  also  forces  the  local(8)  delivery
       agent  to  write  local  and  remote  addresses  from alias expansion to a new queue file,
       instead of attempting to deliver mail to local addresses as soon as they come out of alias
       expansion.

       Writing  local  addresses  from  alias  expansion  to  a  new queue file allows for robust
       handling of temporary delivery errors: errors with one local  member  have  no  effect  on
       deliveries  to  other members of the list.  On the other hand, delivery to local addresses
       as soon as they come out of alias expansion is fragile: a temporary error with  one  local
       address  from  alias expansion will cause the entire alias to be expanded repeatedly until
       the error goes away, or until the message expires in the queue.  In that case,  a  problem
       with one list member results in multiple message deliveries to other list members.

       The  default behavior of Postfix 2.8 and later is to keep the owner-alias attribute of the
       parent alias, when delivering mail to a child alias that  does  not  have  its  own  owner
       alias.  Then,  local  addresses from that child alias will be written to a new queue file,
       and a temporary error with one local address will not affect  delivery  to  other  mailing
       list members.

       Unfortunately, older Postfix releases reset the owner-alias attribute when delivering mail
       to a child alias that does not have its own owner alias. To be precise, this  resets  only
       the  decision to create a new queue file, not the decision to override the envelope sender
       address. The local(8) delivery agent then attempts to deliver local addresses as  soon  as
       they  come  out  of  child  alias  expansion.  If delivery to any address from child alias
       expansion fails with a temporary error condition, the entire mailing list may be  expanded
       repeatedly  until  the  mail expires in the queue, resulting in multiple deliveries of the
       same message to mailing list members.

resolve_dequoted_address (default: yes)

       Resolve a recipient address safely instead of correctly, by looking inside quotes.

       By default, the Postfix address resolver does not quote the address localpart as  per  RFC
       822,  so  that additional @ or % or !  operators remain visible. This behavior is safe but
       it is also technically incorrect.

       If you specify "resolve_dequoted_address = no", then the Postfix resolver  will  not  know
       about  additional  @ etc. operators in the address localpart. This opens opportunities for
       obscure mail relay attacks with user@domain@domain addresses when Postfix provides  backup
       MX service for Sendmail systems.

resolve_null_domain (default: no)

       Resolve  an  address  that  ends  in  the  "@"  null  domain as if the local hostname were
       specified, instead of rejecting the address as invalid.

       This feature is available in Postfix 2.1 and later.  Earlier versions always  resolve  the
       null domain as the local hostname.

       The  Postfix SMTP server uses this feature to reject mail from or to addresses that end in
       the "@" null domain, and from addresses that rewrite into a form that ends in the "@" null
       domain.

resolve_numeric_domain (default: no)

       Resolve  "user@ipaddress"  as  "user@[ipaddress]",  instead  of  rejecting  the address as
       invalid.

       This feature is available in Postfix 2.3 and later.

rewrite_service_name (default: rewrite)

       The name of the address rewriting service. This service  rewrites  addresses  to  standard
       form and resolves them to a (delivery method, next-hop host, recipient) triple.

       This feature is available in Postfix 2.0 and later.

sample_directory (default: /etc/postfix)

       The name of the directory with example Postfix configuration files.  Starting with Postfix
       2.1, these files have been replaced with the postconf(5) manual page.

send_cyrus_sasl_authzid (default: no)

       When authenticating to a remote SMTP or LMTP server with the default setting "no", send no
       SASL  authoriZation  ID (authzid); send only the SASL authentiCation ID (authcid) plus the
       authcid's password.

       The non-default setting "yes" enables the  behavior  of  older  Postfix  versions.   These
       always  send  a  SASL  authzid  that  is  equal  to  the  SASL  authcid,  but  this causes
       interoperability problems with some SMTP servers.

       This feature is available in Postfix 2.4.4 and later.

sender_based_routing (default: no)

       This parameter should not be used. It was replaced by  sender_dependent_relayhost_maps  in
       Postfix version 2.3.

sender_bcc_maps (default: empty)

       Optional  BCC  (blind  carbon-copy) address lookup tables, indexed by sender address.  The
       BCC address (multiple results are not supported) is added when mail enters from outside of
       Postfix.

       Specify  zero  or more "type:name" lookup tables, separated by whitespace or comma. Tables
       will be searched in the specified order until a match is found.

       The table search order is as follows:

       ·      Look up the "user+extension@domain.tld"  address  including  the  optional  address
              extension.

       ·      Look up the "user@domain.tld" address without the optional address extension.

       ·      Look  up  the  "user+extension"  address  local  part when the sender domain equals
              $myorigin, $mydestination, $inet_interfaces or $proxy_interfaces.

       ·      Look up the "user" address local part when  the  sender  domain  equals  $myorigin,
              $mydestination, $inet_interfaces or $proxy_interfaces.

       ·      Look up the "@domain.tld" part.

       Note:  with  Postfix  2.3  and  later the BCC address is added as if it was specified with
       NOTIFY=NONE. The sender will not be notified when the BCC  address  is  undeliverable,  as
       long as all down-stream software implements RFC 3461.

       Note:  with  Postfix  2.2  and earlier the sender will be notified when the BCC address is
       undeliverable.

       Note: automatic BCC recipients are produced only for new mail.   To  avoid  mailer  loops,
       automatic  BCC  recipients  are  not  generated after Postfix forwards mail internally, or
       after Postfix generates mail itself.

       Example:

       sender_bcc_maps = hash:/etc/postfix/sender_bcc

       After a change, run "postmap /etc/postfix/sender_bcc".

       This feature is available in Postfix 2.1 and later.

sender_canonical_classes (default: envelope_sender, header_sender)

       What  addresses  are  subject  to  sender_canonical_maps  address  mapping.   By  default,
       sender_canonical_maps  address  mapping  is  applied  to envelope sender addresses, and to
       header sender addresses.

       Specify one or more of: envelope_sender, header_sender

       This feature is available in Postfix 2.2 and later.

sender_canonical_maps (default: empty)

       Optional address mapping lookup tables for envelope  and  header  sender  addresses.   The
       table format and lookups are documented in canonical(5).

       Example:    you    want    to   rewrite   the   SENDER   address   "user@ugly.domain"   to
       "user@pretty.domain", while still being  able  to  send  mail  to  the  RECIPIENT  address
       "user@ugly.domain".

       Note: $sender_canonical_maps is processed before $canonical_maps.

       Example:

       sender_canonical_maps = hash:/etc/postfix/sender_canonical

sender_dependent_default_transport_maps (default: empty)

       A sender-dependent override for the global default_transport parameter setting. The tables
       are searched by the envelope  sender  address  and  @domain.  A  lookup  result  of  DUNNO
       terminates  the  search without overriding the global default_transport parameter setting.
       This information is overruled with the transport(5) table.

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.  Tables
       will be searched in the specified order until a match is found.

       Note:  this  overrides  default_transport,  not transport_maps, and therefore the expected
       syntax is that of default_transport, not the syntax of transport_maps.  Specifically, this
       does not support the transport_maps syntax for null transport, null nexthop, or null email
       addresses.

       For safety  reasons,  this  feature  does  not  allow  $number  substitutions  in  regular
       expression maps.

       This feature is available in Postfix 2.7 and later.

sender_dependent_relayhost_maps (default: empty)

       A  sender-dependent  override  for  the global relayhost parameter setting. The tables are
       searched by the envelope sender address and @domain. A lookup result of  DUNNO  terminates
       the  search  without  overriding  the  global relayhost parameter setting (Postfix 2.6 and
       later).      This      information      is      overruled      with       relay_transport,
       sender_dependent_default_transport_maps,   default_transport  and  with  the  transport(5)
       table.

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.  Tables
       will be searched in the specified order until a match is found.

       For  safety  reasons,  this  feature  does  not  allow  $number  substitutions  in regular
       expression maps.

       This feature is available in Postfix 2.3 and later.

sendmail_fix_line_endings (default: always)

       Controls how the Postfix  sendmail  command  converts  email  message  line  endings  from
       <CR><LF> into UNIX format (<LF>).

       always Always  convert  message lines ending in <CR><LF>. This setting is the default with
              Postfix 2.9 and later.

       strict Convert message lines ending in <CR><LF> only if  the  first  input  line  ends  in
              <CR><LF>. This setting is backwards-compatible with Postfix 2.8 and earlier.

       never  Never   convert   message  lines  ending  in  <CR><LF>.  This  setting  exists  for
              completeness only.

       This feature is available in Postfix 2.9 and later.

sendmail_path (default: see postconf -d output)

       A Sendmail compatibility feature that specifies the location of  the  Postfix  sendmail(1)
       command. This command can be used to submit mail into the Postfix queue.

service_name (read-only)

       The  master.cf  service  name of a Postfix daemon process. This can be used to distinguish
       the logging from different services that use the same program name.

       Example master.cf entries:

       # Distinguish inbound MTA logging from submission and smtps logging.
       smtp      inet  n       -       n       -       -       smtpd
       submission inet n       -       n       -       -       smtpd
           -o syslog_name=postfix/$service_name
       smtps     inet  n       -       n       -       -       smtpd
           -o syslog_name=postfix/$service_name

       # Distinguish outbound MTA logging from inbound relay logging.
       smtp      unix  -       -       n       -       -       smtp
       relay     unix  -       -       n       -       -       smtp
           -o syslog_name=postfix/$service_name

service_throttle_time (default: 60s)

       How long the  Postfix  master(8)  waits  before  forking  a  server  that  appears  to  be
       malfunctioning.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

setgid_group (default: postdrop)

       The group ownership of set-gid Postfix commands and of group-writable Postfix directories.
       When  this  parameter  value is changed you need to re-run "postfix set-permissions" (with
       Postfix version 2.0 and earlier: "/etc/postfix/post-install set-permissions".

shlib_directory (default: see 'postconf -d' output)

       The location of Postfix dynamically-linked libraries (libpostfix-*.so),  and  the  default
       location  of  Postfix database plugins (postfix-*.so) that have a relative pathname in the
       dynamicmaps.cf  file.   The  shlib_directory  parameter  defaults  to  "no"  when  Postfix
       dynamically-linked  libraries and database plugins are disabled at compile time, otherwise
       it typically defaults to /usr/lib/postfix or /usr/local/lib/postfix.

       Notes:

       ·      The directory specified with shlib_directory should  contain  only  Postfix-related
              files.  Postfix  dynamically-linked  libraries  and  database plugins should not be
              installed in a "public"  system  directory  such  as  /usr/lib  or  /usr/local/lib.
              Linking   Postfix   dynamically-linked  library  files  or  database  plugins  into
              non-Postfix programs is not supported.  Postfix  dynamically-linked  libraries  and
              database  plugins implement a Postfix-internal API that changes without maintaining
              compatibility.

       ·      You can change the shlib_directory value after Postfix is built. However,  you  may
              have to run ldconfig or equivalent to prevent Postfix programs from failing because
              the libpostfix-*.so files are not found.  No ldconfig command is needed if you keep
              the libpostfix-*.so files in the compiled-in default $shlib_directory location.

       This feature is available in Postfix 3.0 and later.

show_user_unknown_table_name (default: yes)

       Display the name of the recipient table in the "User unknown" responses.  The extra detail
       makes trouble shooting easier but also reveals information that is nobody elses business.

       This feature is available in Postfix 2.0 and later.

showq_service_name (default: showq)

       The name of the showq(8) service. This service produces mail queue status reports.

       This feature is available in Postfix 2.0 and later.

smtp_address_preference (default: any)

       The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP client  will  try  first,
       when  a destination has IPv6 and IPv4 addresses with equal MX preference. This feature has
       no effect unless the inet_protocols setting enables both IPv4 and IPv6.

       Postfix SMTP client address preference has  evolved.  With  Postfix  2.8  the  default  is
       "ipv6"; earlier implementations are hard-coded to prefer IPv6 over IPv4.

       Notes for mail delivery between sites that have both IPv4 and IPv6 connectivity:

       ·      The  setting  "smtp_address_preference  =  ipv6" is unsafe.  It can fail to deliver
              mail when there is an outage that affects IPv6,  while  the  destination  is  still
              reachable over IPv4.

       ·      The  setting  "smtp_address_preference  =  any"  is  safe.  With  this,  mail  will
              eventually be delivered even if there is an outage that affects IPv6  or  IPv4,  as
              long as it does not affect both.

       This feature is available in Postfix 2.8 and later.

smtp_address_verify_target (default: rcpt)

       In  the  context  of  email  address verification, the SMTP protocol stage that determines
       whether an email address is deliverable.  Specify one of "rcpt" or "data".  The latter  is
       needed  with  remote  SMTP  servers  that  reject  recipients  after the DATA command. Use
       transport_maps to apply this feature selectively:

           /etc/postfix/main.cf:
               transport_maps = hash:/etc/postfix/transport

           /etc/postfix/transport:
               smtp-domain-that-verifies-after-data    smtp-data-target:
               lmtp-domain-that-verifies-after-data    lmtp-data-target:

           /etc/postfix/master.cf:
               smtp-data-target    unix    -    -    n    -    -    smtp
                   -o smtp_address_verify_target=data
               lmtp-data-target    unix    -    -    n    -    -    lmtp
                   -o lmtp_address_verify_target=data

       Unselective use of the "data" target does no harm, but will result  in  unnecessary  "lost
       connection after DATA" events at remote SMTP/LMTP servers.

       This feature is available in Postfix 3.0 and later.

smtp_always_send_ehlo (default: yes)

       Always send EHLO at the start of an SMTP session.

       With  "smtp_always_send_ehlo  = no", the Postfix SMTP client sends EHLO only when the word
       "ESMTP" appears in the server greeting  banner  (example:  220  spike.porcupine.org  ESMTP
       Postfix).

smtp_balance_inet_protocols (default: yes)

       When  a  remote  destination  resolves to a combination of IPv4 and IPv6 addresses, ensure
       that the Postfix SMTP  client  can  try  both  address  types  before  it  runs  into  the
       smtp_mx_address_limit.

       This  avoids  an  interoperability  problem  when a destination resolves to primarily IPv6
       addresses, the smtp_address_limit feature eliminates most or all IPv4 addresses,  and  the
       destination is not reachable over IPv6.

       This feature is available in Postfix 3.3 and later.

smtp_bind_address (default: empty)

       An  optional  numerical  network  address that the Postfix SMTP client should bind to when
       making an IPv4 connection.

       This can be specified in the main.cf file for all SMTP clients, or it can be specified  in
       the master.cf file for a specific client, for example:

           /etc/postfix/master.cf:
               smtp ... smtp -o smtp_bind_address=11.22.33.44

       Note  1: when inet_interfaces specifies no more than one IPv4 address, and that address is
       a non-loopback address, it is automatically used as the smtp_bind_address.  This  supports
       virtual IP hosting, but can be a problem on multi-homed firewalls. See the inet_interfaces
       documentation for more detail.

       Note 2: address information may be enclosed inside [], but this form is not required here.

smtp_bind_address6 (default: empty)

       An optional numerical network address that the Postfix SMTP client  should  bind  to  when
       making an IPv6 connection.

       This feature is available in Postfix 2.2 and later.

       This  can be specified in the main.cf file for all SMTP clients, or it can be specified in
       the master.cf file for a specific client, for example:

           /etc/postfix/master.cf:
               smtp ... smtp -o smtp_bind_address6=1:2:3:4:5:6:7:8

       Note 1: when inet_interfaces specifies no more than one IPv6 address, and that address  is
       a non-loopback address, it is automatically used as the smtp_bind_address6.  This supports
       virtual IP hosting, but can be a problem on multi-homed firewalls. See the inet_interfaces
       documentation for more detail.

       Note  2:  address  information may be enclosed inside [], but this form is not recommended
       here.

smtp_body_checks (default: empty)

       Restricted body_checks(5) tables for the Postfix SMTP client.  These tables  are  searched
       while  mail  is being delivered.  Actions that change the delivery time or destination are
       not available.

       This feature is available in Postfix 2.5 and later.

smtp_cname_overrides_servername (default: version dependent)

       When the remote SMTP servername is a DNS CNAME, replace the  servername  with  the  result
       from  CNAME  expansion  for  the  purpose  of  logging,  SASL  password lookup, TLS policy
       decisions,  or  TLS   certificate   verification.   The   value   "no"   hardens   Postfix
       smtp_tls_per_site  hostname-based policies against false hostname information in DNS CNAME
       records, and makes SASL password file  lookups  more  predictable.  This  is  the  default
       setting as of Postfix 2.3.

       When  DNS  CNAME  records  are validated with secure DNS lookups (smtp_dns_support_level =
       dnssec), they are always allowed to  override  the  above  servername  (Postfix  2.11  and
       later).

       This feature is available in Postfix 2.2.9 and later.

smtp_connect_timeout (default: 30s)

       The  Postfix  SMTP  client  time  limit  for completing a TCP connection, or zero (use the
       operating system built-in time limit).

       When no connection can be made within the deadline, the Postfix SMTP client tries the next
       address on the mail exchanger list. Specify 0 to disable the time limit (i.e. use whatever
       timeout is implemented by the operating system).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_connection_cache_destinations (default: empty)

       Permanently  enable  SMTP  connection  caching  for the specified destinations.  With SMTP
       connection caching, a connection is not closed immediately  after  completion  of  a  mail
       transaction.      Instead,     the     connection    is    kept    open    for    up    to
       $smtp_connection_cache_time_limit seconds.  This allows connections to be reused for other
       deliveries, and can improve mail delivery performance.

       Specify a comma or white space separated list of destinations or pseudo-destinations:

       ·      if  mail  is  sent  without  a relay host: a domain name (the right-hand side of an
              email address, without the [] around a numeric IP address),

       ·      if mail is sent via a relay host: a relay host name (without [] or non-default  TCP
              port), as specified in main.cf or in the transport map,

       ·      if mail is sent via a UNIX-domain socket: a pathname (without the unix: prefix),

       ·      a /file/name with domain names and/or relay host names as defined above,

       ·      a  "type:table"  with  domain  names and/or relay host names on the left-hand side.
              The right-hand side result from "type:table" lookups is ignored.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_on_demand (default: yes)

       Temporarily enable SMTP connection caching while a destination has a high volume  of  mail
       in the active queue.  With SMTP connection caching, a connection is not closed immediately
       after completion of a mail transaction.  Instead, the connection is kept open  for  up  to
       $smtp_connection_cache_time_limit seconds.  This allows connections to be reused for other
       deliveries, and can improve mail delivery performance.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_time_limit (default: 2s)

       When SMTP connection caching is enabled, the amount of time that  an  unused  SMTP  client
       socket  is kept open before it is closed.  Do not specify larger values without permission
       from the remote sites.

       This feature is available in Postfix 2.2 and later.

smtp_connection_reuse_count_limit (default: 0)

       When SMTP connection caching is enabled, the number of times that an SMTP session  may  be
       reused  before  it  is  closed,  or  zero  (no  limit).   With a reuse count limit of N, a
       connection is used up to N+1 times.

       NOTE: This feature is unsafe. When a high-volume destination has  multiple  inbound  MTAs,
       then  the slowest inbound MTA will attract the most connections to that destination.  This
       limitation does not exist with the smtp_connection_reuse_time_limit feature.

       This feature is available in Postfix 2.11.

smtp_connection_reuse_time_limit (default: 300s)

       The amount of time during which Postfix will use an SMTP connection repeatedly.  The timer
       starts  when  the connection is initiated (i.e. it includes the connect, greeting and helo
       latency, in addition to the latencies of subsequent mail delivery transactions).

       This feature addresses a performance stability problem  with  remote  SMTP  servers.  This
       problem is not specific to Postfix: it can happen when any MTA sends large amounts of SMTP
       email to a site that has multiple MX hosts.

       The problem starts when one of a set of MX hosts  becomes  slower  than  the  rest.   Even
       though  SMTP clients connect to fast and slow MX hosts with equal probability, the slow MX
       host ends up with more simultaneous inbound connections than the faster MX hosts,  because
       the slow MX host needs more time to serve each client request.

       The  slow  MX  host becomes a connection attractor.  If one MX host becomes N times slower
       than the rest, it dominates mail delivery latency unless there are more  than  N  fast  MX
       hosts  to  counter  the  effect. And if the number of MX hosts is smaller than N, the mail
       delivery latency becomes effectively that of the slowest MX  host  divided  by  the  total
       number of MX hosts.

       The  solution  uses connection caching in a way that differs from Postfix version 2.2.  By
       limiting the amount of time during which a connection can be used repeatedly  (instead  of
       limiting  the  number  of  deliveries  over  that  connection),  Postfix not only restores
       fairness in the distribution of simultaneous connections across a set of MX hosts, it also
       favors deliveries over connections that perform well, which is exactly what we want.

       The default reuse time limit, 300s, is comparable to the various smtp transaction timeouts
       which are fair estimates of maximum excess latency for a slow delivery.  Note  that  hosts
       may  accept  thousands  of messages over a single connection within the default connection
       reuse time limit. This number is much larger than the default Postfix version 2.2 limit of
       10  messages  per  cached  connection.  It may prove necessary to lower the limit to avoid
       interoperability issues with MTAs that exhibit bugs when many messages are delivered via a
       single  connection.  A lower reuse time limit risks losing the benefit of connection reuse
       when the average connection and mail delivery latency exceeds the reuse time limit.

       This feature is available in Postfix 2.3 and later.

smtp_data_done_timeout (default: 600s)

       The Postfix SMTP client time limit for sending the SMTP ".", and for receiving the  remote
       SMTP server response.

       When no response is received within the deadline, a warning is logged that the mail may be
       delivered multiple times.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_data_init_timeout (default: 120s)

       The  Postfix  SMTP  client time limit for sending the SMTP DATA command, and for receiving
       the remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_data_xfer_timeout (default: 180s)

       The  Postfix  SMTP  client  time  limit  for  sending  the SMTP message content.  When the
       connection makes no progress for more than  $smtp_data_xfer_timeout  seconds  the  Postfix
       SMTP client terminates the transfer.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

smtp_defer_if_no_mx_address_found (default: no)

       Defer mail delivery when no MX record resolves to an IP address.

       The default (no) is to return the mail as undeliverable. With older Postfix  versions  the
       default  was to keep trying to deliver the mail until someone fixed the MX record or until
       the mail was too old.

       Note: the Postfix SMTP client always ignores MX records with  equal  or  worse  preference
       than the local MTA itself.

       This feature is available in Postfix 2.1 and later.

smtp_delivery_status_filter (default: $default_delivery_status_filter)

       Optional  filter  for  the  smtp(8)  delivery  agent to change the delivery status code or
       explanatory    text     of     successful     or     unsuccessful     deliveries.      See
       default_delivery_status_filter for details.

       NOTE:  This  feature  modifies Postfix SMTP client error or non-error messages that may or
       may not be derived from remote SMTP server responses.  In contrast, the  smtp_reply_filter
       feature modifies remote SMTP server responses only.

smtp_destination_concurrency_limit (default: $default_destination_concurrency_limit)

       The  maximal  number  of  parallel deliveries to the same destination via the smtp message
       delivery transport. This limit is enforced by the  queue  manager.  The  message  delivery
       transport name is the first field in the entry in the master.cf file.

smtp_destination_recipient_limit (default: $default_destination_recipient_limit)

       The maximal number of recipients per message for the smtp message delivery transport. This
       limit is enforced by the queue manager. The message delivery transport name is  the  first
       field in the entry in the master.cf file.

       Setting    this    parameter    to    a    value    of    1   changes   the   meaning   of
       smtp_destination_concurrency_limit  from  concurrency  per  domain  into  concurrency  per
       recipient.

smtp_discard_ehlo_keyword_address_maps (default: empty)

       Lookup  tables,  indexed by the remote SMTP server address, with case insensitive lists of
       EHLO keywords (pipelining, starttls, auth, etc.) that the Postfix SMTP client will  ignore
       in  the  EHLO  response  from  a  remote  SMTP  server. See smtp_discard_ehlo_keywords for
       details.   The   table   is   not   indexed   by    hostname    for    consistency    with
       smtpd_discard_ehlo_keyword_address_maps.

       Specify  zero  or more "type:name" lookup tables, separated by whitespace or comma. Tables
       will be searched in the specified order until a match is found.

       This feature is available in Postfix 2.2 and later.

smtp_discard_ehlo_keywords (default: empty)

       A case insensitive list of EHLO keywords  (pipelining,  starttls,  auth,  etc.)  that  the
       Postfix SMTP client will ignore in the EHLO response from a remote SMTP server.

       This feature is available in Postfix 2.2 and later.

       Notes:

       ·      Specify the silent-discard pseudo keyword to prevent this action from being logged.

       ·      Use  the  smtp_discard_ehlo_keyword_address_maps  feature  to discard EHLO keywords
              selectively.

smtp_dns_reply_filter (default: empty)

       Optional filter for Postfix SMTP client DNS lookup results.  Specify zero or  more  lookup
       tables.  The lookup tables are searched in the given order for a match with the DNS lookup
       result, converted to the following form:

           name ttl class type preference value

       The class field is always "IN", the preference field exists only for MX records, the names
       of hosts, domains, etc.  end in ".", and those names are in ASCII form (xn--mumble form in
       the case of UTF8 names).

       When a match is found, the table lookup result specifies an action.  By default, the table
       query  and  the  action  name  are case-insensitive.  Currently, only the IGNORE action is
       implemented.

       Notes:

       ·      Postfix  DNS  reply  filters  have  no  effect  on  implicit  DNS  lookups  through
              nsswitch.conf or equivalent mechanisms.

       ·      The  Postfix  SMTP/LMTP client uses smtp_dns_reply_filter and lmtp_dns_reply_filter
              only to discover a remote SMTP or LMTP service (record  types  MX,  A,  AAAAA,  and
              TLSA).     These    lookups    are    also   made   to   implement   the   features
              reject_unverified_sender and reject_unverified_recipient.

       ·      The Postfix SMTP/LMTP client defers mail delivery when a filter removes all  lookup
              results from a successful query.

       ·      Postfix  SMTP  server uses smtpd_dns_reply_filter only to look up MX, A, AAAAA, and
              TXT   records   to    implement    the    features    reject_unknown_helo_hostname,
              reject_unknown_sender_domain,  reject_unknown_recipient_domain,  reject_rbl_*,  and
              reject_rhsbl_*.

       ·      The Postfix SMTP server logs a warning  or  defers  mail  delivery  when  a  filter
              removes all lookup results from a successful query.

       Example:  ignore  Google  AAAA  records in Postfix SMTP client DNS lookups, because Google
       sometimes hard-rejects mail from IPv6 clients with valid PTR etc. records.

       /etc/postfix/main.cf:
           smtp_dns_reply_filter = pcre:/etc/postfix/smtp_dns_reply_filter

       /etc/postfix/smtp_dns_reply_filter:
           # /domain ttl IN AAAA address/ action, all case-insensitive.
           # Note: the domain name ends in ".".
           /^\S+\.google\.com\.\s+\S+\s+\S+\s+AAAA\s+/ IGNORE

       This feature is available in Postfix 3.0 and later.

smtp_dns_resolver_options (default: empty)

       DNS Resolver options for the Postfix SMTP client.  Specify zero or more of  the  following
       options,  separated by comma or whitespace.  Option names are case-sensitive. Some options
       refer to domain names that are specified in the file /etc/resolv.conf or equivalent.

       res_defnames
              Append the current domain name to single-component names (those that do not contain
              a  "."  character).  This  can  produce  incorrect  results,  and is the hard-coded
              behavior prior to Postfix 2.8.

       res_dnsrch
              Search for host names in the current domain and in parent domains. This can produce
              incorrect results and is therefore not recommended.

       This feature is available in Postfix 2.8 and later.

smtp_dns_support_level (default: empty)

       Level  of  DNS  support in the Postfix SMTP client.  With "smtp_dns_support_level" left at
       its empty default value, the legacy "disable_dns_lookups" parameter controls  whether  DNS
       is enabled in the Postfix SMTP client, otherwise the legacy parameter is ignored.

       Specify one of the following:

       disabled
              Disable  DNS  lookups.  No MX lookups are performed and hostname to address lookups
              are unconditionally "native".  This setting  is  not  appropriate  for  hosts  that
              deliver  mail  to  the  public  Internet.  Some obsolete how-to documents recommend
              disabling DNS lookups in some configurations  with  content_filters.   This  is  no
              longer required and strongly discouraged.

       enabled
              Enable  DNS  lookups.   Nexthop  destination  domains  not enclosed in "[]" will be
              subject  to  MX  lookups.   If   "dns"   and   "native"   are   included   in   the
              "smtp_host_lookup"  parameter value, DNS will be queried first to resolve MX-host A
              records, followed by "native" lookups if no answer is found in DNS.

       dnssec Enable DNSSEC lookups.  The "dnssec" setting differs  from  the  "enabled"  setting
              above in the following ways:

       ·      Any   MX   lookups   will   set   RES_USE_DNSSEC   and   RES_USE_EDNS0  to  request
              DNSSEC-validated  responses.  If  the   MX   response   is   DNSSEC-validated   the
              corresponding hostnames are considered validated.

       ·      The  address lookups of validated hostnames are also validated, (provided of course
              "smtp_host_lookup" includes "dns", see below).

       ·      Temporary failures  in  DNSSEC-enabled  hostname-to-address  resolution  block  any
              "native"  lookups.   Additional  "native"  lookups  only happen when DNSSEC lookups
              hard-fail (NODATA or NXDOMAIN).

       The Postfix SMTP client considers non-MX  "[nexthop]"  and  "[nexthop]:port"  destinations
       equivalent  to  statically-validated  MX  records of the form "nexthop.  IN MX 0 nexthop."
       Therefore, with "dnssec" support turned on, validated hostname-to-address lookups apply to
       the  nexthop domain of any "[nexthop]" or "[nexthop]:port" destination.  This is also true
       for LMTP "inet:host" and  "inet:host:port"  destinations,  as  LMTP  hostnames  are  never
       subject to MX lookups.

       The  "dnssec"  setting  is  recommended  only if you plan to use the dane or dane-only TLS
       security level,  otherwise  enabling  DNSSEC  support  in  Postfix  offers  no  additional
       security.   Postfix  DNSSEC  support  relies  on  an  upstream  recursive  nameserver that
       validates DNSSEC signatures.  Such  a  DNS  server  will  always  filter  out  forged  DNS
       responses, even when Postfix itself is not configured to use DNSSEC.

       When  using Postfix DANE support the "smtp_host_lookup" parameter should include "dns", as
       DANE is not applicable to hosts resolved via "native" lookups.

       As mentioned above, Postfix is not a validating stub resolver; it relies on  the  system's
       configured DNSSEC-validating recursive nameserver to perform all DNSSEC validation.  Since
       this nameserver's DNSSEC-validated  responses  will  be  fully  trusted,  it  is  strongly
       recommended  that the MTA host have a local DNSSEC-validating recursive caching nameserver
       listening on a loopback address, and be configured to use only  this  nameserver  for  all
       lookups.   Otherwise,  Postfix  may remain subject to man-in-the-middle attacks that forge
       responses from the recursive nameserver

       DNSSEC support requires a version of Postfix  compiled  against  a  reasonably-modern  DNS
       resolver(3) library that implements the RES_USE_DNSSEC and RES_USE_EDNS0 resolver options.

       This feature is available in Postfix 2.11 and later.

smtp_enforce_tls (default: no)

       Enforcement mode: require that remote SMTP servers use TLS encryption, and never send mail
       in the clear.  This also requires  that  the  remote  SMTP  server  hostname  matches  the
       information  in the remote server certificate, and that the remote SMTP server certificate
       was issued by a CA that is trusted by the Postfix SMTP client. If the certificate  doesn't
       verify or the hostname doesn't match, delivery is deferred and mail stays in the queue.

       The   server   hostname  is  matched  against  all  names  provided  as  dNSNames  in  the
       SubjectAlternativeName.  If no dNSNames are specified, the  CommonName  is  checked.   The
       behavior may be changed with the smtp_tls_enforce_peername option.

       This  option  is  useful  only  if  you  are definitely sure that you will only connect to
       servers that support RFC 2487 _and_ that provide valid server certificates.   Typical  use
       is for clients that send all their email to a dedicated mailhub.

       This  feature  is  available  in  Postfix  2.2  and  later. With Postfix 2.3 and later use
       smtp_tls_security_level instead.

smtp_fallback_relay (default: $fallback_relay)

       Optional list of relay hosts for SMTP  destinations  that  can't  be  found  or  that  are
       unreachable. With Postfix 2.2 and earlier this parameter is called fallback_relay.

       By  default,  mail is returned to the sender when a destination is not found, and delivery
       is deferred when a destination is unreachable.

       With bulk email deliveries, it can be beneficial to run the fallback relay MTA on the same
       host,  so  that  it  can  reuse the sender IP address.  This speeds up deliveries that are
       delayed by IP-based reputation systems (greylist, etc.).

       The fallback relays  must  be  SMTP  destinations.  Specify  a  domain,  host,  host:port,
       [host]:port,  [address]  or  [address]:port; the form [host] turns off MX lookups.  If you
       specify multiple SMTP destinations, Postfix will try them in the specified order.

       To prevent mailer loops between MX hosts and fall-back  hosts,  Postfix  version  2.2  and
       later  will  not use the fallback relays for destinations that it is MX host for (assuming
       DNS lookup is turned on).

smtp_generic_maps (default: empty)

       Optional lookup tables  that  perform  address  rewriting  in  the  Postfix  SMTP  client,
       typically  to transform a locally valid address into a globally valid address when sending
       mail across the Internet.  This is needed when the local machine does  not  have  its  own
       Internet domain name, but uses something like localdomain.local instead.

       Specify  zero  or more "type:name" lookup tables, separated by whitespace or comma. Tables
       will be searched in the specified order until a match is found.

       The table format and lookups are documented in  generic(5);  examples  are  shown  in  the
       ADDRESS_REWRITING_README and STANDARD_CONFIGURATION_README documents.

       This feature is available in Postfix 2.2 and later.

smtp_header_checks (default: empty)

       Restricted header_checks(5) tables for the Postfix SMTP client.  These tables are searched
       while mail is being delivered.  Actions that change the delivery time or  destination  are
       not available.

       This feature is available in Postfix 2.5 and later.

smtp_helo_name (default: $myhostname)

       The hostname to send in the SMTP HELO or EHLO command.

       The default value is the machine hostname.  Specify a hostname or [ip.add.re.ss].

       This  information  can be specified in the main.cf file for all SMTP clients, or it can be
       specified in the master.cf file for a specific client, for example:

           /etc/postfix/master.cf:
               mysmtp ... smtp -o smtp_helo_name=foo.bar.com

       This feature is available in Postfix 2.0 and later.

smtp_helo_timeout (default: 300s)

       The Postfix SMTP client time limit for sending the HELO or EHLO command, and for receiving
       the initial remote SMTP server response.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

smtp_host_lookup (default: dns)

       What mechanisms the Postfix SMTP client uses  to  look  up  a  host's  IP  address.   This
       parameter  is  ignored  when  DNS  lookups  are  disabled  (see:  disable_dns_lookups  and
       smtp_dns_support_level).  The "dns" mechanism is always tried before "native" if both  are
       listed.

       Specify one of the following:

       dns    Hosts can be found in the DNS (preferred).

       native Use the native naming service only (nsswitch.conf, or equivalent mechanism).

       dns, native
              Use the native service for hosts not found in the DNS.

       This feature is available in Postfix 2.1 and later.

smtp_line_length_limit (default: 998)

       The  maximal length of message header and body lines that Postfix will send via SMTP. This
       limit does not include the <CR><LF> at the end of each line.  Longer lines are  broken  by
       inserting "<CR><LF><SPACE>", to minimize the damage to MIME formatted mail.

       The  Postfix  limit  of  998 characters not including <CR><LF> is consistent with the SMTP
       limit of 1000 characters including <CR><LF>.  The Postfix limit was 990 with  Postfix  2.8
       and earlier.

smtp_mail_timeout (default: 300s)

       The  Postfix  SMTP  client time limit for sending the MAIL FROM command, and for receiving
       the remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_mime_header_checks (default: empty)

       Restricted  mime_header_checks(5)  tables  for  the  Postfix SMTP client. These tables are
       searched while mail is  being  delivered.   Actions  that  change  the  delivery  time  or
       destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_mx_address_limit (default: 5)

       The  maximal  number of MX (mail exchanger) IP addresses that can result from Postfix SMTP
       client mail exchanger lookups, or zero (no limit). Prior  to  Postfix  version  2.3,  this
       limit was disabled by default.

       This feature is available in Postfix 2.1 and later.

smtp_mx_session_limit (default: 2)

       The  maximal  number  of SMTP sessions per delivery request before the Postfix SMTP client
       gives up or delivers to a fall-back relay host,  or  zero  (no  limit).  This  restriction
       ignores sessions that fail to complete the SMTP initial handshake (Postfix version 2.2 and
       earlier) or that fail to complete the EHLO and TLS  handshake  (Postfix  version  2.3  and
       later).

       This feature is available in Postfix 2.1 and later.

smtp_nested_header_checks (default: empty)

       Restricted  nested_header_checks(5)  tables  for the Postfix SMTP client. These tables are
       searched while mail is  being  delivered.   Actions  that  change  the  delivery  time  or
       destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_never_send_ehlo (default: no)

       Never  send  EHLO  at  the  start  of  an SMTP session. See also the smtp_always_send_ehlo
       parameter.

smtp_per_record_deadline (default: no)

       Change the behavior of the smtp_*_timeout time limits, from a time limit per read or write
       system  call,  to a time limit to send or receive a complete record (an SMTP command line,
       SMTP response line, SMTP message content line, or TLS protocol message).  This limits  the
       impact from hostile peers that trickle data one byte at a time.

       Note:  when  per-record deadlines are enabled, a short timeout may cause problems with TLS
       over very slow network connections.  The reasons are that a TLS protocol message can be up
       to  16  kbytes  long (with TLSv1), and that an entire TLS protocol message must be sent or
       received within the per-record deadline.

       This feature is available in Postfix 2.9 and  later.  With  older  Postfix  releases,  the
       behavior is as if this parameter is set to "no".

smtp_pix_workaround_delay_time (default: 10s)

       How long the Postfix SMTP client pauses before sending ".<CR><LF>" in order to work around
       the PIX firewall "<CR><LF>.<CR><LF>" bug.

       Choosing a too short time makes this workaround ineffective when  sending  large  messages
       over slow network connections.

smtp_pix_workaround_maps (default: empty)

       Lookup tables, indexed by the remote SMTP server address, with per-destination workarounds
       for CISCO PIX firewall bugs.  The table is not indexed by hostname  for  consistency  with
       smtp_discard_ehlo_keyword_address_maps.

       Specify  zero  or more "type:name" lookup tables, separated by whitespace or comma. Tables
       will be searched in the specified order until a match is found.

       This feature is available in Postfix 2.4 and later.

smtp_pix_workaround_threshold_time (default: 500s)

       How long a message must be queued before the Postfix SMTP client turns on the PIX firewall
       "<CR><LF>.<CR><LF>"  bug  workaround for delivery through firewalls with "smtp fixup" mode
       turned on.

       By default, the workaround is turned off for  mail  that  is  queued  for  less  than  500
       seconds.  In  other  words,  the  workaround is normally turned off for the first delivery
       attempt.

       Specify 0 to enable the PIX firewall "<CR><LF>.<CR><LF>" bug  workaround  upon  the  first
       delivery attempt.

smtp_pix_workarounds (default: disable_esmtp, delay_dotcrlf)

       A  list  that  specifies  zero  or  more  workarounds  for  CISCO PIX firewall bugs. These
       workarounds are implemented by the Postfix SMTP client. Workaround names are separated  by
       comma  or  space,  and are case insensitive.  This parameter setting can be overruled with
       per-destination smtp_pix_workaround_maps settings.

       delay_dotcrlf
              Insert a delay before sending ".<CR><LF>" after the end  of  the  message  content.
              The    delay    is    subject    to    the    smtp_pix_workaround_delay_time    and
              smtp_pix_workaround_threshold_time parameter settings.

       disable_esmtp
              Disable all extended SMTP commands: send HELO instead of EHLO.

       This feature is available in Postfix 2.4 and later. The  default  settings  are  backwards
       compatible with earlier Postfix versions.

smtp_quit_timeout (default: 300s)

       The  Postfix  SMTP  client  time limit for sending the QUIT command, and for receiving the
       remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_quote_rfc821_envelope (default: yes)

       Quote  addresses  in Postfix SMTP client MAIL FROM and RCPT TO commands as required by RFC
       5321. This includes putting quotes around an address localpart that ends in ".".

       The default is to comply with RFC 5321. If you have to send mail to a broken SMTP  server,
       configure a special SMTP client in master.cf:

           /etc/postfix/master.cf:
               broken-smtp . . . smtp -o smtp_quote_rfc821_envelope=no

       and  route mail for the destination in question to the "broken-smtp" message delivery with
       a transport(5) table.

       This feature is available in Postfix 2.1 and later.

smtp_randomize_addresses (default: yes)

       Randomize the order of equal-preference MX host addresses.  This is a performance  feature
       of the Postfix SMTP client.

smtp_rcpt_timeout (default: 300s)

       The Postfix SMTP client time limit for sending the SMTP RCPT TO command, and for receiving
       the remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtp_reply_filter (default: empty)

       A  mechanism  to transform replies from remote SMTP servers one line at a time.  This is a
       last-resort tool to work around  server  replies  that  break  interoperability  with  the
       Postfix  SMTP  client.   Other  uses involve fault injection to test Postfix's handling of
       invalid responses.

       Notes:

       ·      In the case of a multi-line reply, the Postfix SMTP client  uses  the  final  reply
              line's numerical SMTP reply code and enhanced status code.

       ·      The  numerical SMTP reply code (XYZ) takes precedence over the enhanced status code
              (X.Y.Z).  When the enhanced status code initial digit differs from the  SMTP  reply
              code  initial  digit,  or when no enhanced status code is present, the Postfix SMTP
              client uses a generic enhanced status code (X.0.0) instead.

       Specify the name of a "type:table" lookup table. The search string is a single SMTP  reply
       line  as  received  from  the  remote  SMTP  server, except that the trailing <CR><LF> are
       removed.  When the lookup succeeds, the result replaces the single SMTP reply line.

       Examples:

       /etc/postfix/main.cf:
           smtp_reply_filter = pcre:/etc/postfix/reply_filter

       /etc/postfix/reply_filter:
           # Transform garbage into "250-filler..." so that it looks like
           # one line from a multi-line reply. It does not matter what we
           # substitute here as long it has the right syntax.  The Postfix
           # SMTP client will use the final line's numerical SMTP reply
           # code and enhanced status code.
           !/^([2-5][0-9][0-9]($|[- ]))/ 250-filler for garbage

       This feature is available in Postfix 2.7.

smtp_rset_timeout (default: 20s)

       The Postfix SMTP client time limit for sending the RSET command,  and  for  receiving  the
       remote  SMTP  server  response.  The SMTP client sends RSET in order to finish a recipient
       address probe, or to verify that a cached session is still usable.

       This feature is available in Postfix 2.1 and later.

smtp_sasl_auth_cache_name (default: empty)

       An optional table to prevent repeated SASL authentication failures with  the  same  remote
       SMTP  server  hostname,  username  and  password.  Each table (key, value) pair contains a
       server name, a username and password, and the full server response.  This  information  is
       stored  when a remote SMTP server rejects an authentication attempt with a 535 reply code.
       As long as the smtp_sasl_password_maps information does no change,  and  as  long  as  the
       smtp_sasl_auth_cache_name  information does not expire (see smtp_sasl_auth_cache_time) the
       Postfix SMTP client avoids SASL authentication attempts with the same server, username and
       password,    and    instead    bounces   or   defers   mail   as   controlled   with   the
       smtp_sasl_auth_soft_bounce configuration parameter.

       Use    a    per-destination    delivery     concurrency     of     1     (for     example,
       "smtp_destination_concurrency_limit   =  1",  "relay_destination_concurrency_limit  =  1",
       etc.), otherwise multiple delivery agents may experience a login failure at the same time.

       The table must be accessed via the proxywrite service, i.e. the map name must  start  with
       "proxy:". The table should be stored under the directory specified with the data_directory
       parameter.

       This feature uses cryptographic hashing to protect plain-text passwords, and requires that
       Postfix is compiled with TLS support.

       Example:

       smtp_sasl_auth_cache_name = proxy:btree:/var/lib/postfix/sasl_auth_cache

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_cache_time (default: 90d)

       The maximal age of an smtp_sasl_auth_cache_name entry before it is removed.

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_enable (default: no)

       Enable  SASL  authentication  in  the  Postfix  SMTP client.  By default, the Postfix SMTP
       client uses no authentication.

       Example:

       smtp_sasl_auth_enable = yes

smtp_sasl_auth_soft_bounce (default: yes)

       When a remote SMTP server rejects a SASL authentication request with  a  535  reply  code,
       defer  mail  delivery  instead of returning mail as undeliverable. The latter behavior was
       hard-coded prior to Postfix version 2.5.

       Note: the setting "yes" overrides the global soft_bounce parameter, but the  setting  "no"
       does not.

       Example:

       # Default as of Postfix 2.5
       smtp_sasl_auth_soft_bounce = yes
       # The old hard-coded default
       smtp_sasl_auth_soft_bounce = no

       This feature is available in Postfix 2.5 and later.

smtp_sasl_mechanism_filter (default: empty)

       If  non-empty,  a  Postfix SMTP client filter for the remote SMTP server's list of offered
       SASL mechanisms.  Different  client  and  server  implementations  may  support  different
       mechanism lists; by default, the Postfix SMTP client will use the intersection of the two.
       smtp_sasl_mechanism_filter specifies an optional third mechanism list to intersect with.

       Specify  mechanism  names,  "/file/name"  patterns  or  "type:table"  lookup  tables.  The
       right-hand side result from "type:table" lookups is ignored. Specify "!pattern" to exclude
       a mechanism name from the list. The  form  "!/file/name"  is  supported  only  in  Postfix
       version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

       Examples:

       smtp_sasl_mechanism_filter = plain, login
       smtp_sasl_mechanism_filter = /etc/postfix/smtp_mechs
       smtp_sasl_mechanism_filter = !gssapi, !login, static:rest

smtp_sasl_password_maps (default: empty)

       Optional  Postfix  SMTP  client lookup tables with one username:password entry per sender,
       remote hostname or next-hop domain. Per-sender lookup is done only  when  sender-dependent
       authentication  is enabled.  If no username:password entry is found, then the Postfix SMTP
       client will not attempt to authenticate to the remote host.

       The Postfix SMTP client opens the lookup table before going to chroot  jail,  so  you  can
       leave the password file in /etc/postfix.

       Specify  zero  or more "type:name" lookup tables, separated by whitespace or comma. Tables
       will be searched in the specified order until a match is found.

smtp_sasl_path (default: empty)

       Implementation-specific information that the Postfix SMTP client  passes  through  to  the
       SASL  plug-in  implementation  that  is  selected  with  smtp_sasl_type.   Typically  this
       specifies the name of a configuration file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

smtp_sasl_security_options (default: noplaintext, noanonymous)

       Postfix SMTP client SASL security options;  as  of  Postfix  2.3  the  list  of  available
       features depends on the SASL client implementation that is selected with smtp_sasl_type.

       The following security features are defined for the cyrus client SASL implementation:

       Specify zero or more of the following:

       noplaintext
              Disallow methods that use plaintext passwords.

       noactive
              Disallow methods subject to active (non-dictionary) attack.

       nodictionary
              Disallow methods subject to passive (dictionary) attack.

       noanonymous
              Disallow methods that allow anonymous authentication.

       mutual_auth
              Only  allow  methods  that  provide  mutual authentication (not available with SASL
              version 1).

       Example:

       smtp_sasl_security_options = noplaintext

smtp_sasl_tls_security_options (default: $smtp_sasl_security_options)

       The SASL authentication security options  that  the  Postfix  SMTP  client  uses  for  TLS
       encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtp_sasl_tls_verified_security_options (default: $smtp_sasl_tls_security_options)

       The  SASL  authentication  security  options  that  the  Postfix  SMTP client uses for TLS
       encrypted SMTP sessions with a verified server certificate.

       When mail is sent to the public MX host for the recipient's  domain,  server  certificates
       are by default optional, and delivery proceeds even if certificate verification fails. For
       delivery via a submission service that requires SASL authentication, it may be appropriate
       to  send  plaintext passwords only when the connection to the server is strongly encrypted
       and the server identity is verified.

       The smtp_sasl_tls_verified_security_options parameter makes it  possible  to  only  enable
       plaintext  mechanisms  when  a  secure  connection  to the server is available. Submission
       servers subject to this policy must either have verifiable certificates or offer  suitable
       non-plaintext SASL mechanisms.

       This feature is available in Postfix 2.6 and later.

smtp_sasl_type (default: cyrus)

       The  SASL  plug-in  type  that the Postfix SMTP client should use for authentication.  The
       available types are listed with the "postconf -A" command.

       This feature is available in Postfix 2.3 and later.

smtp_send_dummy_mail_auth (default: no)

       Whether  or  not  to  append  the  "AUTH=<>"  option  to  the   MAIL   FROM   command   in
       SASL-authenticated  SMTP sessions. The default is not to send this, to avoid problems with
       broken  remote   SMTP   servers.    Before   Postfix   2.9   the   behavior   is   as   if
       "smtp_send_dummy_mail_auth = yes".

       This feature is available in Postfix 2.9 and later.

smtp_send_xforward_command (default: no)

       Send  the  non-standard  XFORWARD  command  when  the  Postfix  SMTP  server EHLO response
       announces XFORWARD support.

       This allows a Postfix SMTP delivery agent, used for injecting mail into a content  filter,
       to forward the name, address, protocol and HELO name of the original client to the content
       filter and downstream queuing SMTP server. This  can  produce  more  useful  logging  than
       localhost[127.0.0.1] etc.

       This feature is available in Postfix 2.1 and later.

smtp_sender_dependent_authentication (default: no)

       Enable  sender-dependent authentication in the Postfix SMTP client; this is available only
       with SASL authentication, and disables SMTP connection caching to ensure  that  mail  from
       different senders will use the appropriate credentials.

       This feature is available in Postfix 2.3 and later.

smtp_skip_4xx_greeting (default: yes)

       Skip SMTP servers that greet with a 4XX status code (go away, try again later).

       By  default,  the  Postfix  SMTP  client  moves  on  the  next  mail  exchanger.   Specify
       "smtp_skip_4xx_greeting = no" if Postfix should defer delivery immediately.

       This feature is available in Postfix 2.0 and earlier.  Later Postfix versions always  skip
       remote SMTP servers that greet with a 4XX status code.

smtp_skip_5xx_greeting (default: yes)

       Skip remote SMTP servers that greet with a 5XX status code.

       By   default,  the  Postfix  SMTP  client  moves  on  the  next  mail  exchanger.  Specify
       "smtp_skip_5xx_greeting = no" if Postfix should bounce the mail immediately. Caution:  the
       latter behavior appears to contradict RFC 2821.

smtp_skip_quit_response (default: yes)

       Do not wait for the response to the SMTP QUIT command.

smtp_starttls_timeout (default: 300s)

       Time  limit  for  Postfix  SMTP  client  write  and read operations during TLS startup and
       shutdown handshake procedures.

       This feature is available in Postfix 2.2 and later.

smtp_tcp_port (default: smtp)

       The default TCP port that the Postfix SMTP client connects to.  Specify  a  symbolic  name
       (see services(5)) or a numeric port.

smtp_tls_CAfile (default: empty)

       A  file  containing  CA certificates of root CAs trusted to sign either remote SMTP server
       certificates or intermediate CA certificates.  These are loaded  into  memory  before  the
       smtp(8)  client  enters the chroot jail. If the number of trusted roots is large, consider
       using smtp_tls_CApath instead, but note that the latter directory must be present  in  the
       chroot  jail  if the smtp(8) client is chrooted. This file may also be used to augment the
       client certificate trust chain, but it is best to include all  the  required  certificates
       directly in $smtp_tls_cert_file.

       Specify  "smtp_tls_CAfile  =  /path/to/system_CA_file"  to  use  ONLY  the system-supplied
       default Certification Authority certificates.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending the system-supplied
       default CAs and trusting third-party certificates.

       Example:

       smtp_tls_CAfile = /etc/postfix/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_CApath (default: empty)

       Directory  with  PEM  format  Certification  Authority  certificates that the Postfix SMTP
       client uses to verify a remote SMTP  server  certificate.   Don't  forget  to  create  the
       necessary "hash" links with, for example, "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs".

       To  use  this  option in chroot mode, this directory (or a copy) must be inside the chroot
       jail.

       Specify "smtp_tls_CApath = /path/to/system_CA_directory" to use ONLY  the  system-supplied
       default Certification Authority certificates.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending the system-supplied
       default CAs and trusting third-party certificates.

       Example:

       smtp_tls_CApath = /etc/postfix/certs

       This feature is available in Postfix 2.2 and later.

smtp_tls_block_early_mail_reply (default: no)

       Try  to  detect  a  mail  hijacking  attack  based  on  a   TLS   protocol   vulnerability
       (CVE-2009-3555), where an attacker prepends malicious HELO, MAIL, RCPT, DATA commands to a
       Postfix SMTP client TLS session.  The attack would succeed with non-Postfix  SMTP  servers
       that  reply to the malicious HELO, MAIL, RCPT, DATA commands after negotiating the Postfix
       SMTP client TLS session.

       This feature is available in Postfix 2.7.

smtp_tls_cert_file (default: empty)

       File with the Postfix SMTP client RSA certificate in  PEM  format.   This  file  may  also
       contain  the Postfix SMTP client private RSA key, and these may be the same as the Postfix
       SMTP server RSA certificate and key file.

       Do not configure client certificates unless you must present client  TLS  certificates  to
       one or more servers. Client certificates are not usually needed, and can cause problems in
       configurations that work well without them. The recommended setting is to let the defaults
       stand:

           smtp_tls_cert_file =
           smtp_tls_key_file =
           smtp_tls_dcert_file =
           smtp_tls_dkey_file =
           smtp_tls_eccert_file =
           smtp_tls_eckey_file =

       The best way to use the default settings is to comment out the above parameters in main.cf
       if present.

       To enable remote SMTP servers to verify the Postfix SMTP client certificate,  the  issuing
       CA  certificates  must  be  made  available to the server. You should include the required
       certificates in the client certificate  file,  the  client  certificate  first,  then  the
       issuing CA(s) (bottom-up order).

       Example:  the  certificate  for "client.example.com" was issued by "intermediate CA" which
       itself has a certificate issued by "root  CA".   Create  the  client.pem  file  with  "cat
       client_cert.pem intermediate_CA.pem root_CA.pem > client.pem".

       If  you  also  want to verify remote SMTP server certificates issued by these CAs, you can
       add the CA certificates to the smtp_tls_CAfile, in which case it is not necessary to  have
       them in the smtp_tls_cert_file, smtp_tls_dcert_file or smtp_tls_eccert_file.

       A certificate supplied here must be usable as an SSL client certificate and hence pass the
       "openssl verify -purpose sslclient ..." test.

       Example:

       smtp_tls_cert_file = /etc/postfix/client.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_cipherlist (default: empty)

       Obsolete Postfix < 2.3 control for the Postfix  SMTP  client  TLS  cipher  list.  As  this
       feature applies to all TLS security levels, it is easy to create interoperability problems
       by choosing a non-default cipher list. Do not use a non-default TLS cipher list  on  hosts
       that  deliver  email  to  the public Internet: you will be unable to send email to servers
       that only support the ciphers you exclude. Using a restricted  cipher  list  may  be  more
       appropriate  for  an  internal MTA, where one can exert some control over the TLS software
       and settings of the peer servers.

       Note: do not use "" quotes around the parameter value.

       This feature is available in Postfix version 2.2. It is not  used  with  Postfix  2.3  and
       later; use smtp_tls_mandatory_ciphers instead.

smtp_tls_ciphers (default: medium)

       The  minimum TLS cipher grade that the Postfix SMTP client will use with opportunistic TLS
       encryption. Cipher types listed in smtp_tls_exclude_ciphers are  excluded  from  the  base
       definition  of  the  selected  cipher  grade.    The default value is "medium" for Postfix
       releases after the middle of 2015, "export" for older releases.

       When TLS is mandatory the  cipher  grade  is  chosen  via  the  smtp_tls_mandatory_ciphers
       configuration  parameter,  see  there  for  syntax  details.  See smtp_tls_policy_maps for
       information on how to configure ciphers on a per-destination basis.

       This feature is available in Postfix 2.6 and later. With earlier Postfix releases only the
       smtp_tls_mandatory_ciphers  parameter  is  implemented,  and opportunistic TLS always uses
       "export" or better (i.e. all) ciphers.

smtp_tls_dane_insecure_mx_policy (default: dane)

       The TLS policy for MX hosts with  "secure"  TLSA  records  when  the  nexthop  destination
       security  level  is  dane,  but  the MX record was found via an "insecure" MX lookup.  The
       choices are:

       may    The TLSA records will be ignored and TLS will be optional.  If the MX host does not
              appear  to  support  STARTTLS, or the STARTTLS handshake fails, mail may be sent in
              the clear.

       encrypt
              The TLSA records will signal a requirement to use TLS.  While TLS  encryption  will
              be required, authentication will not be performed.

       dane (default)
              The  TLSA  records  will  be used just as with "secure" MX records.  TLS encryption
              will be  required,  and,  if  at  least  one  of  the  TLSA  records  is  "usable",
              authentication  will  be required.  When authentication succeeds, it will be logged
              only as "Trusted", not "Verified", because the MX host name could have been forged.
              Though with "insecure" MX records an active attacker can compromise SMTP  transport
              security  by  returning  forged MX records, such attacks are "tamper-evident" since
              any forged MX hostnames will be recorded in the mail logs.  Attackers who  place  a
              high value staying hidden may be deterred from forging MX records.

       This feature is available in Postfix 3.1 and later. The may policy is backwards-compatible
       with earlier Postfix versions.

smtp_tls_dcert_file (default: empty)

       File with the Postfix SMTP client DSA certificate in  PEM  format.   This  file  may  also
       contain the Postfix SMTP client private DSA key.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_dcert_file = /etc/postfix/client-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_dkey_file (default: $smtp_tls_dcert_file)

       File  with  the  Postfix  SMTP  client  DSA  private  key in PEM format.  This file may be
       combined  with  the  Postfix   SMTP   client   DSA   certificate   file   specified   with
       $smtp_tls_dcert_file.

       The  private  key must be accessible without a pass-phrase, i.e. it must not be encrypted.
       File permissions should grant read-only access to the system superuser  account  ("root"),
       and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtp_tls_eccert_file (default: empty)

       File  with  the  Postfix  SMTP client ECDSA certificate in PEM format.  This file may also
       contain the Postfix SMTP client ECDSA private key.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_eccert_file = /etc/postfix/ecdsa-ccert.pem

       This feature is available in Postfix 2.6 and later, when Postfix is  compiled  and  linked
       with OpenSSL 1.0.0 or later.

smtp_tls_eckey_file (default: $smtp_tls_eccert_file)

       File  with  the  Postfix  SMTP  client  ECDSA private key in PEM format.  This file may be
       combined  with  the  Postfix  SMTP  client   ECDSA   certificate   file   specified   with
       $smtp_tls_eccert_file.

       The  private  key must be accessible without a pass-phrase, i.e. it must not be encrypted.
       File permissions should grant read-only access to the system superuser  account  ("root"),
       and no access to anyone else.

       This  feature  is  available in Postfix 2.6 and later, when Postfix is compiled and linked
       with OpenSSL 1.0.0 or later.

smtp_tls_enforce_peername (default: yes)

       With mandatory TLS encryption, require that the remote SMTP server  hostname  matches  the
       information  in  the  remote SMTP server certificate.  As of RFC 2487 the requirements for
       hostname checking for MTA clients are not specified.

       This option can be set to "no" to disable strict peer name checking. This setting  has  no
       effect on sessions that are controlled via the smtp_tls_per_site table.

       Disabling the hostname verification can make sense in closed environment where special CAs
       are created.  If not used carefully, this option opens the danger of a "man-in-the-middle"
       attack (the CommonName of this attacker will be logged).

       This  feature  is  available  in  Postfix  2.2  and  later. With Postfix 2.3 and later use
       smtp_tls_security_level instead.

smtp_tls_exclude_ciphers (default: empty)

       List of ciphers or cipher types to exclude from the Postfix SMTP client cipher list at all
       TLS  security  levels. This is not an OpenSSL cipherlist, it is a simple list separated by
       whitespace and/or commas. The elements are a single cipher, or one or more  "+"  separated
       cipher properties, in which case only ciphers matching all the properties are excluded.

       Examples (some of these will cause problems):

           smtp_tls_exclude_ciphers = aNULL
           smtp_tls_exclude_ciphers = MD5, DES
           smtp_tls_exclude_ciphers = DES+MD5
           smtp_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
           smtp_tls_exclude_ciphers = kEDH+aRSA

       The  first setting, disables anonymous ciphers. The next setting disables ciphers that use
       the MD5 digest algorithm or the  (single)  DES  encryption  algorithm.  The  next  setting
       disables ciphers that use MD5 and DES together.  The next setting disables the two ciphers
       "AES256-SHA" and "DES-CBC3-MD5". The last setting disables  ciphers  that  use  "EDH"  key
       exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtp_tls_fingerprint_cert_match (default: empty)

       List  of  acceptable remote SMTP server certificate fingerprints for the "fingerprint" TLS
       security  level  (smtp_tls_security_level  =  fingerprint).  At   this   security   level,
       Certification  Authorities  are  not  used,  and certificate expiration times are ignored.
       Instead, server certificates are verified directly via their  certificate  fingerprint  or
       public key fingerprint (Postfix 2.9 and later). The fingerprint is a message digest of the
       server  certificate  (or  public  key).  The  digest  algorithm  is   selected   via   the
       smtp_tls_fingerprint_digest parameter.

       When  an  smtp_tls_policy_maps table entry specifies the "fingerprint" security level, any
       "match" attributes  in  that  entry  specify  the  list  of  valid  fingerprints  for  the
       corresponding destination. Multiple fingerprints can be combined with a "|" delimiter in a
       single match attribute, or multiple match attributes can be employed.

       Example:  Certificate  fingerprint  verification  with  internal  mailhub.   Two  matching
       fingerprints   are  listed.  The  relayhost  may  be  multiple  physical  hosts  behind  a
       load-balancer,  each  with  its  own  private/public  key  and  self-signed   certificate.
       Alternatively,  a  single  relayhost  may  be  in the process of switching from one set of
       private/public keys to another, and both keys are trusted just prior to the transition.

           relayhost = [mailhub.example.com]
           smtp_tls_security_level = fingerprint
           smtp_tls_fingerprint_digest = md5
           smtp_tls_fingerprint_cert_match =
               3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
               EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       Example: Certificate fingerprint verification  with  selected  destinations.   As  in  the
       example above, we show two matching fingerprints:

           /etc/postfix/main.cf:
               smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
               smtp_tls_fingerprint_digest = md5

           /etc/postfix/tls_policy:
               example.com fingerprint
                   match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
                   match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.5 and later.

smtp_tls_fingerprint_digest (default: md5)

       The   message   digest   algorithm  used  to  construct  remote  SMTP  server  certificate
       fingerprints.  At  the  "fingerprint"  TLS  security  level   (smtp_tls_security_level   =
       fingerprint),  the  server  certificate  is  verified by directly matching its certificate
       fingerprint or its public key fingerprint (Postfix 2.9 and later). The fingerprint is  the
       message digest of the server certificate (or its public key) using the selected algorithm.
       With a digest algorithm resistant to "second pre-image" attacks, it  is  not  feasible  to
       create  a  new public key and a matching certificate (or public/private key-pair) that has
       the same fingerprint.

       The default algorithm is md5; this is consistent with the backwards compatible setting  of
       the digest used to verify client certificates in the SMTP server.

       The  best  practice  algorithm is now sha1. Recent advances in hash function cryptanalysis
       have led to md5 being deprecated in favor of sha1.  However, as long as there are no known
       "second  pre-image"  attacks  against md5, its use in this context can still be considered
       safe.

       While additional digest algorithms are often  available  with  OpenSSL's  libcrypto,  only
       those  used  by  libssl  in SSL cipher suites are available to Postfix. For now this means
       just md5 or sha1.

       To find the fingerprint of a specific certificate file, with a specific digest  algorithm,
       run:

           $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The text to the right of "=" sign is the desired fingerprint.  For example:

           $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
           SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       To  extract  the public key fingerprint from an X.509 certificate, you need to extract the
       public key from the certificate and compute the appropriate  digest  of  its  DER  (ASN.1)
       encoding.  With OpenSSL the "-pubkey" option of the "x509" command extracts the public key
       always in "PEM" format. We pipe the result to another OpenSSL command  that  converts  the
       key to DER and then to the "dgst" command to compute the fingerprint.

       The  actual  command  to transform the key to DER format depends on the version of OpenSSL
       used. With OpenSSL 1.0.0 and later, the  "pkey"  command  supports  all  key  types.  With
       OpenSSL  0.9.8  and  earlier, the key type is always RSA (nobody uses DSA, and EC keys are
       not fully supported by 0.9.8), so the "rsa" command is used.

           # OpenSSL 1.0 with all certificates and SHA-1 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl pkey -pubin -outform DER |
               openssl dgst -sha1 -c
           (stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:8b:fc:09:1a:61:98:b5:bc:7c:60:58

           # OpenSSL 0.9.8 with RSA certificates and MD5 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl rsa -pubin -outform DER |
               openssl dgst -md5 -c
           (stdin)= f4:62:60:f6:12:8f:d5:8d:28:4d:13:a7:db:b2:ff:50

       The Postfix SMTP server and client log the peer (leaf) certificate fingerprint and  public
       key fingerprint when the TLS loglevel is 2 or higher.

       Note:  Postfix  2.9.0-2.9.5  computed  the  public  key  fingerprint  incorrectly.  To use
       public-key fingerprints, upgrade to Postfix 2.9.6 or later.

       This feature is available in Postfix 2.5 and later.

smtp_tls_force_insecure_host_tlsa_lookup (default: no)

       Lookup the associated DANE TLSA RRset even when a hostname is not an alias and its address
       records lie in an unsigned zone.  This is unlikely to ever yield DNSSEC validated results,
       since child zones of unsigned zones are also unsigned in the absence  of  DLV  or  locally
       configured  non-root  trust-anchors.   We anticipate that such mechanisms will not be used
       for just the "_tcp" subdomain of a  host.   Suppressing  the  TLSA  RRset  lookup  reduces
       latency and avoids potential interoperability problems with nameservers for unsigned zones
       that are not prepared to handle the new TLSA RRset.

       This feature is available in Postfix 2.11.

smtp_tls_key_file (default: $smtp_tls_cert_file)

       File with the Postfix SMTP client RSA private  key  in  PEM  format.   This  file  may  be
       combined   with   the   Postfix   SMTP   client   RSA   certificate  file  specified  with
       $smtp_tls_cert_file.

       The private key must be accessible without a pass-phrase, i.e. it must not  be  encrypted.
       File  permissions  should grant read-only access to the system superuser account ("root"),
       and no access to anyone else.

       Example:

       smtp_tls_key_file = $smtp_tls_cert_file

       This feature is available in Postfix 2.2 and later.

smtp_tls_loglevel (default: 0)

       Enable additional Postfix SMTP client logging of TLS activity.  Each  logging  level  also
       includes the information that is logged at a lower logging level.

              0 Disable logging of TLS activity.

              1  Log  only  a  summary message on TLS handshake completion - no logging of remote
              SMTP server certificate  trust-chain  verification  errors  if  server  certificate
              verification  is  not  required.   With  Postfix  2.8  and earlier, log the summary
              message and unconditionally log trust-chain verification errors.

              2 Also log levels during TLS negotiation.

              3 Also log hexadecimal and ASCII dump of TLS negotiation process.

              4 Also log hexadecimal and ASCII dump of complete transmission after STARTTLS.

       Do not use "smtp_tls_loglevel = 2" or higher except in case of problems. Use of loglevel 4
       is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtp_tls_mandatory_ciphers (default: medium)

       The  minimum  TLS  cipher  grade  that the Postfix SMTP client will use with mandatory TLS
       encryption.  The default value "medium" is suitable for most destinations with  which  you
       may  want  to  enforce  TLS, and is beyond the reach of today's cryptanalytic methods. See
       smtp_tls_policy_maps for information on how to  configure  ciphers  on  a  per-destination
       basis.

       The following cipher grades are supported:

       export Enable  "EXPORT"  grade  or  better  OpenSSL ciphers.  The underlying cipherlist is
              specified via the tls_export_cipherlist  configuration  parameter,  which  you  are
              strongly encouraged to not change.  This choice is insecure and SHOULD NOT be used.

       low    Enable  "LOW"  grade  or  better  OpenSSL  ciphers.   The  underlying cipherlist is
              specified  via  the  tls_low_cipherlist  configuration  parameter,  which  you  are
              strongly encouraged to not change.  This choice is insecure and SHOULD NOT be used.

       medium Enable  "MEDIUM"  grade  or  better  OpenSSL ciphers.  The underlying cipherlist is
              specified via the tls_medium_cipherlist  configuration  parameter,  which  you  are
              strongly encouraged to not change.

       high   Enable only "HIGH" grade OpenSSL ciphers.  This setting may be appropriate when all
              mandatory TLS destinations (e.g. when all mail is  routed  to  a  suitably  capable
              relayhost)  support  at least one "HIGH" grade cipher. The underlying cipherlist is
              specified via  the  tls_high_cipherlist  configuration  parameter,  which  you  are
              strongly encouraged to not change.

       null   Enable  only  the  "NULL"  OpenSSL  ciphers,  these  provide authentication without
              encryption.  This setting is only appropriate in the rare case that all servers are
              prepared  to  use  NULL  ciphers (not normally enabled in TLS servers). A plausible
              use-case is an LMTP server listening on a UNIX-domain socket that is configured  to
              support   "NULL"   ciphers.   The   underlying  cipherlist  is  specified  via  the
              tls_null_cipherlist configuration parameter, which you are strongly  encouraged  to
              not change.

       The  underlying  cipherlists  for  grades other than "null" include anonymous ciphers, but
       these are automatically filtered out if the Postfix SMTP client is  configured  to  verify
       server certificates.  You are very unlikely to need to take any steps to exclude anonymous
       ciphers, they are excluded automatically as necessary.   If  you  must  exclude  anonymous
       ciphers  at  the "may" or "encrypt" security levels, when the Postfix SMTP client does not
       need or  use  peer  certificates,  set  "smtp_tls_exclude_ciphers  =  aNULL".  To  exclude
       anonymous  ciphers  only  when  TLS is enforced, set "smtp_tls_mandatory_exclude_ciphers =
       aNULL".

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_exclude_ciphers (default: empty)

       Additional list of ciphers or cipher types to exclude from the Postfix SMTP client  cipher
       list  at  mandatory  TLS  security  levels.  This list works in addition to the exclusions
       listed with smtp_tls_exclude_ciphers (see there for syntax details).

       Starting with Postfix  2.6,  the  mandatory  cipher  exclusions  can  be  specified  on  a
       per-destination basis via the TLS policy "exclude" attribute. See smtp_tls_policy_maps for
       notes and examples.

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_protocols (default: !SSLv2, !SSLv3)

       List of SSL/TLS protocols that the  Postfix  SMTP  client  will  use  with  mandatory  TLS
       encryption.   In  main.cf the values are separated by whitespace, commas or colons. In the
       policy table "protocols" attribute (see smtp_tls_policy_maps) the only valid separator  is
       colon.  An  empty  value  means  allow  all  protocols.  The  valid  protocol  names, (see
       \fBfBSSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1". The default value is  "!SSLv2,
       !SSLv3" for Postfix releases after the middle of 2015, "!SSLv2" for older releases.

       With  Postfix >= 2.5 the parameter syntax was expanded to support protocol exclusions. One
       can explicitly exclude "SSLv2" by  setting  "smtp_tls_mandatory_protocols  =  !SSLv2".  To
       exclude  both  "SSLv2"  and  "SSLv3"  set "smtp_tls_mandatory_protocols = !SSLv2, !SSLv3".
       Listing the protocols to include, rather than protocols to exclude, is supported, but  not
       recommended.  The  exclusion  form  more  closely matches the underlying OpenSSL interface
       semantics.

       The range of protocols advertised by  an  SSL/TLS  client  must  be  contiguous.   When  a
       protocol version is enabled, disabling any higher version implicitly disables all versions
       above that higher version.  Thus, for example:

           smtp_tls_mandatory_protocols = !SSLv2, !TLSv1
       also disables any protocols version higher than TLSv1 leaving only "SSLv3" enabled.

       Note: As of OpenSSL 1.0.1 two new protocols are defined,  "TLSv1.1"  and  "TLSv1.2".  When
       Postfix  <= 2.5 is linked against OpenSSL 1.0.1 or later, these, or any other new protocol
       versions, cannot be disabled except by also  disabling  "TLSv1"  (typically  leaving  just
       "SSLv3").   The latest patch levels of Postfix >= 2.6, and all versions of Postfix >= 2.10
       can explicitly disable support for "TLSv1.1" or "TLSv1.2".

       At the dane and dane-only security levels, when usable TLSA records are obtained  for  the
       remote  SMTP server, the Postfix SMTP client is obligated to include the SNI TLS extension
       in its SSL client hello message.  This may help the remote SMTP  server  live  up  to  its
       promise  to  provide  a  certificate  that matches its TLSA records.  Since TLS extensions
       require TLS 1.0 or later, the Postfix SMTP client must disable "SSLv2"  and  "SSLv3"  when
       SNI  is  required.   If you use "dane" or "dane-only" do not disable TLSv1, except perhaps
       via the policy table for destinations  which  you  are  sure  will  support  "TLSv1.1"  or
       "TLSv1.2".

       See  the  documentation  of  the  smtp_tls_policy_maps  parameter  and TLS_README for more
       information about security levels.

       Example:

       # Preferred syntax with Postfix >= 2.5:
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       # Legacy syntax:
       smtp_tls_mandatory_protocols = TLSv1

       This feature is available in Postfix 2.3 and later.

smtp_tls_note_starttls_offer (default: no)

       Log the hostname of a remote SMTP server that offers STARTTLS, when  TLS  is  not  already
       enabled for that server.

       The logfile record looks like:

       postfix/smtp[pid]:  Host offered STARTTLS: [name.of.host]

       This feature is available in Postfix 2.2 and later.

smtp_tls_per_site (default: empty)

       Optional  lookup  tables  with  the  Postfix  SMTP  client  TLS  usage  policy by next-hop
       destination and by remote SMTP server hostname.   When  both  lookups  succeed,  the  more
       specific  per-site policy (NONE, MUST, etc) overrides the less specific one (MAY), and the
       more secure per-site policy (MUST, etc)  overrides  the  less  secure  one  (NONE).   With
       Postfix  2.3 and later smtp_tls_per_site is strongly discouraged: use smtp_tls_policy_maps
       instead.

       Use of the bare hostname as the per-site table lookup key is discouraged. Always  use  the
       full  destination  nexthop  (enclosed  in  [] with a possible ":port" suffix). A recipient
       domain or MX-enabled transport next-hop with no port suffix may look like a bare hostname,
       but is still a suitable destination.

       Specify  a next-hop destination or server hostname on the left-hand side; no wildcards are
       allowed. The next-hop destination is either  the  recipient  domain,  or  the  destination
       specified  with  a  transport(5)  table,  the  relayhost parameter, or the relay_transport
       parameter.  On the right hand side specify one of the following keywords:

       NONE   Don't use TLS at all. This overrides a less specific MAY  lookup  result  from  the
              alternate  host  or  next-hop  lookup  key,  and overrides the global smtp_use_tls,
              smtp_enforce_tls, and smtp_tls_enforce_peername settings.

       MAY    Try to use TLS if the server  announces  support,  otherwise  use  the  unencrypted
              connection.  This  has less precedence than a more specific result (including NONE)
              from the alternate host or next-hop lookup key, and has less  precedence  than  the
              more specific global "smtp_enforce_tls = yes" or "smtp_tls_enforce_peername = yes".

       MUST_NOPEERMATCH
              Require  TLS  encryption,  but  do not require that the remote SMTP server hostname
              matches the information in the remote SMTP server certificate, or that  the  server
              certificate was issued by a trusted CA. This overrides a less secure NONE or a less
              specific MAY lookup result from the alternate host  or  next-hop  lookup  key,  and
              overrides  the  global smtp_use_tls, smtp_enforce_tls and smtp_tls_enforce_peername
              settings.

       MUST   Require TLS encryption, require that the remote SMTP server  hostname  matches  the
              information in the remote SMTP server certificate, and require that the remote SMTP
              server certificate was issued by a trusted CA. This overrides a  less  secure  NONE
              and  MUST_NOPEERMATCH  or a less specific MAY lookup result from the alternate host
              or next-hop lookup key, and overrides the global smtp_use_tls, smtp_enforce_tls and
              smtp_tls_enforce_peername settings.

       The above keywords correspond to the "none", "may", "encrypt" and "verify" security levels
       for the new smtp_tls_security_level parameter introduced in  Postfix  2.3.  Starting  with
       Postfix    2.3,    and    independently    of   how   the   policy   is   specified,   the
       smtp_tls_mandatory_ciphers and  smtp_tls_mandatory_protocols  parameters  apply  when  TLS
       encryption is mandatory. Connections for which encryption is optional typically enable all
       "export" grade and better ciphers (see smtp_tls_ciphers and smtp_tls_protocols).

       As long as no secure DNS lookup mechanism is available, false hostnames  in  MX  or  CNAME
       responses  can  change  the  server  hostname  that Postfix uses for TLS policy lookup and
       server certificate verification. Even with a perfect match between the server hostname and
       the  server  certificate,  there  is  no  guarantee that Postfix is connected to the right
       server.  See TLS_README (Closing a DNS loophole with obsolete per-site TLS policies) for a
       possible work-around.

       This  feature  is  available  in  Postfix  2.2  and  later. With Postfix 2.3 and later use
       smtp_tls_policy_maps instead.

smtp_tls_policy_maps (default: empty)

       Optional lookup tables with the Postfix  SMTP  client  TLS  security  policy  by  next-hop
       destination;   when   a   non-empty  value  is  specified,  this  overrides  the  obsolete
       smtp_tls_per_site parameter.  See  TLS_README  for  a  more  detailed  discussion  of  TLS
       security levels.

       Specify  zero  or more "type:name" lookup tables, separated by whitespace or comma. Tables
       will be searched in the specified order until a match is found.

       The TLS policy table is indexed by the full next-hop  destination,  which  is  either  the
       recipient   domain,   or   the   verbatim  next-hop  specified  in  the  transport  table,
       $local_transport,  $virtual_transport,  $relay_transport   or   $default_transport.   This
       includes any enclosing square brackets and any non-default destination server port suffix.
       The LMTP socket type prefix (inet: or unix:) is not included in the lookup key.

       Only the next-hop domain, or $myhostname with LMTP over UNIX-domain sockets,  is  used  as
       the  nexthop name for certificate verification. The port and any enclosing square brackets
       are used in the table lookup key, but are not used for server name verification.

       When the lookup key is a domain name without enclosing square brackets or any :port suffix
       (typically  the  recipient domain), and the full domain is not found in the table, just as
       with the transport(5) table, the parent domain starting with  a  leading  "."  is  matched
       recursively.  This  allows one to specify a security policy for a recipient domain and all
       its sub-domains.

       The lookup result is a security level, followed by an optional list of  whitespace  and/or
       comma  separated  name=value  attributes  that  override related main.cf settings. The TLS
       security levels in order of increasing security are:

       none   No TLS. No additional attributes are supported at this level.

       may    Opportunistic TLS. Since sending in the clear  is  acceptable,  demanding  stronger
              than  default TLS security merely reduces interoperability. The optional "ciphers",
              "exclude" and "protocols" attributes (available for opportunistic TLS with  Postfix
              >=   2.6)   override   the   "smtp_tls_ciphers",   "smtp_tls_exclude_ciphers"   and
              "smtp_tls_protocols" configuration parameters. When  opportunistic  TLS  handshakes
              fail,  Postfix retries the connection with TLS disabled.  This allows mail delivery
              to sites with non-interoperable TLS implementations.

       encrypt
              Mandatory TLS encryption. At  this  level  and  higher,  the  optional  "protocols"
              attribute   overrides   the  main.cf  smtp_tls_mandatory_protocols  parameter,  the
              optional  "ciphers"  attribute  overrides  the  main.cf  smtp_tls_mandatory_ciphers
              parameter,  and  the  optional  "exclude"  attribute (Postfix >= 2.6) overrides the
              main.cf smtp_tls_mandatory_exclude_ciphers parameter. In the policy table, multiple
              protocols  or excluded ciphers must be separated by colons, as attribute values may
              not contain whitespace or commas.

       dane   Opportunistic DANE TLS.  The TLS policy for the destination is  obtained  via  TLSA
              records in DNSSEC.  If no TLSA records are found, the effective security level used
              is may.  If TLSA records are found, but none are  usable,  the  effective  security
              level  is  encrypt.   When  usable  TLSA  records  are obtained for the remote SMTP
              server, the server certificate must match the TLSA records.  RFC  7672  (DANE)  TLS
              authentication and DNSSEC support is available with Postfix 2.11 and later.

       dane-only
              Mandatory  DANE  TLS.   The  TLS  policy  for  the destination is obtained via TLSA
              records in DNSSEC.  If no TLSA records are found, or none are usable, no connection
              is  made  to the server.  When usable TLSA records are obtained for the remote SMTP
              server, the server certificate must match the TLSA records.  RFC  7672  (DANE)  TLS
              authentication and DNSSEC support is available with Postfix 2.11 and later.

       fingerprint
              Certificate fingerprint verification. Available with Postfix 2.5 and later. At this
              security level, there are no trusted  Certification  Authorities.  The  certificate
              trust  chain,  expiration  date,  ...  are not checked. Instead, the optional match
              attribute, or else the main.cf smtp_tls_fingerprint_cert_match parameter, lists the
              certificate  fingerprints  or the public key fingerprint (Postfix 2.9 and later) of
              the  valid  server  certificate.  The  digest  algorithm  used  to  calculate   the
              fingerprint  is  selected  by  the  smtp_tls_fingerprint_digest parameter. Multiple
              fingerprints can be combined with a "|" delimiter in a single match  attribute,  or
              multiple  match  attributes  can  be  employed.  The ":" character is not used as a
              delimiter as it occurs between each pair of fingerprint (hexadecimal) digits.

       verify Mandatory TLS verification.  At this security level, DNS MX lookups are trusted  to
              be  secure  enough,  and  the  name  verified  in the server certificate is usually
              obtained indirectly via unauthenticated  DNS  MX  lookups.   The  optional  "match"
              attribute overrides the main.cf smtp_tls_verify_cert_match parameter. In the policy
              table, multiple match patterns and strategies must  be  separated  by  colons.   In
              practice  explicit  control  over matching is more common with the "secure" policy,
              described below.

       secure Secure-channel TLS. At this security level, DNS MX lookups, though potentially used
              to  determine  the  candidate  next-hop gateway IP addresses, are not trusted to be
              secure enough for TLS peername verification. Instead, the default name verified  in
              the  server  certificate  is  obtained directly from the next-hop, or is explicitly
              specified  via  the  optional  match  attribute   which   overrides   the   main.cf
              smtp_tls_secure_cert_match  parameter. In the policy table, multiple match patterns
              and strategies must be separated by colons.  The match  attribute  is  most  useful
              when  multiple  domains  are  supported  by  common  server, the policy entries for
              additional domains specify matching rules for the primary domain certificate. While
              transport table overrides routing the secondary domains to the primary nexthop also
              allow secure verification, they risk delivery to the wrong destination when domains
              change  hands  or  are  re-assigned  to  new  gateways.  With the "match" attribute
              approach, routing is not perturbed, and mail is deferred if verification of  a  new
              MX host fails.

       Example:

       /etc/postfix/main.cf:
           smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
           # Postfix 2.5 and later
           smtp_tls_fingerprint_digest = md5

       /etc/postfix/tls_policy:
           example.edu                 none
           example.mil                 may
           example.gov                 encrypt protocols=TLSv1
           example.com                 verify ciphers=high
           example.net                 secure
           .example.net                secure match=.example.net:example.net
           [mail.example.org]:587      secure match=nexthop
           # Postfix 2.5 and later
           [thumb.example.org]          fingerprint
               match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
               match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1

       Note:    The    hostname    strategy    if    listed   in   a   non-default   setting   of
       smtp_tls_secure_cert_match or in the match attribute in the policy table  can  render  the
       secure   level   vulnerable  to  DNS  forgery.  Do  not  use  the  hostname  strategy  for
       secure-channel configurations in environments where DNS security is not assured.

       This feature is available in Postfix 2.3 and later.

smtp_tls_protocols (default: !SSLv2, !SSLv3)

       List of TLS  protocols  that  the  Postfix  SMTP  client  will  exclude  or  include  with
       opportunistic  TLS  encryption. The default value is "!SSLv2, !SSLv3" for Postfix releases
       after the middle of 2015, "!SSLv2" for older releases. Before  Postfix  2.6,  the  Postfix
       SMTP client would use all protocols with opportunistic TLS.

       In  main.cf  the values are separated by whitespace, commas or colons. In the policy table
       (see smtp_tls_policy_maps) the only valid separator is colon. An empty value  means  allow
       all  protocols.  The  valid  protocol  names,  (see \fBfBSSL_get_version(3)), are "SSLv2",
       "SSLv3" and "TLSv1".

       The range of protocols advertised by  an  SSL/TLS  client  must  be  contiguous.   When  a
       protocol version is enabled, disabling any higher version implicitly disables all versions
       above that higher version.  Thus, for example:

           smtp_tls_mandatory_protocols = !SSLv2, !TLSv1
       also disables any protocols version higher than TLSv1 leaving only "SSLv3" enabled.

       Note: As of OpenSSL 1.0.1 two new protocols are  defined,  "TLSv1.1"  and  "TLSv1.2".  The
       latest  patch levels of Postfix >= 2.6, and all versions of Postfix >= 2.10 can explicitly
       disable support for "TLSv1.1" or "TLSv1.2"

       To include a protocol list its name, to exclude it, prefix the name with a "!"  character.
       To  exclude SSLv2 for opportunistic TLS set "smtp_tls_protocols = !SSLv2". To exclude both
       "SSLv2" and "SSLv3" set "smtp_tls_protocols =  !SSLv2,  !SSLv3".  Explicitly  listing  the
       protocols to include, rather than protocols to exclude, is supported, but not recommended.
       The exclusion form more closely matches the underlying OpenSSL interface semantics.

       Example:
       # TLSv1 or better:
       smtp_tls_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.6 and later.

smtp_tls_scert_verifydepth (default: 9)

       The verification depth for remote SMTP server certificates. A depth of 1 is sufficient  if
       the issuing CA is listed in a local CA file.

       The  default  verification depth is 9 (the OpenSSL default) for compatibility with earlier
       Postfix behavior. Prior to Postfix 2.5, the default value was 5, but  the  limit  was  not
       actually  enforced.  If  you have set this to a lower non-default value, certificates with
       longer trust chains may now fail to verify. Certificate chains with 1 or 2 CAs are common,
       deeper chains are more rare and any number between 5 and 9 should suffice in practice. You
       can choose a lower number if, for example, you trust certificates directly  signed  by  an
       issuing CA but not any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtp_tls_secure_cert_match (default: nexthop, dot-nexthop)

       How  the Postfix SMTP client verifies the server certificate peername for the "secure" TLS
       security level. In a "secure" TLS policy table ($smtp_tls_policy_maps) entry the  optional
       "match" attribute overrides this main.cf setting.

       This  parameter  specifies  one  or  more  patterns  or  strategies  separated  by commas,
       whitespace or colons.  In  the  policy  table  the  only  valid  separator  is  the  colon
       character.

       For  a  description  of the pattern and strategy syntax see the smtp_tls_verify_cert_match
       parameter. The "hostname" strategy should be avoided in this context, as in the absence of
       a  secure  global  DNS, using the results of MX lookups in certificate verification is not
       immune to active (man-in-the-middle) attacks on DNS.

       Sample main.cf setting:

           smtp_tls_secure_cert_match = nexthop

       Sample policy table override:

           example.net     secure match=example.com:.example.com
           .example.net    secure match=example.com:.example.com

       This feature is available in Postfix 2.3 and later.

smtp_tls_security_level (default: empty)

       The default SMTP TLS security level for the Postfix SMTP client; when a non-empty value is
       specified,  this  overrides  the  obsolete  parameters smtp_use_tls, smtp_enforce_tls, and
       smtp_tls_enforce_peername.

       Specify one of the following security levels:

       none   No TLS. TLS  will  not  be  used  unless  enabled  for  specific  destinations  via
              smtp_tls_policy_maps.

       may    Opportunistic  TLS.  Use  TLS  if  this  is  supported  by  the remote SMTP server,
              otherwise use plaintext. Since  sending  in  the  clear  is  acceptable,  demanding
              stronger   than   default   TLS  security  merely  reduces  interoperability.   The
              "smtp_tls_ciphers"  and  "smtp_tls_protocols"  (Postfix   >=   2.6)   configuration
              parameters   provide  control  over  the  protocols  and  cipher  grade  used  with
              opportunistic TLS.  With earlier releases the opportunistic  TLS  cipher  grade  is
              always  "export"  and  no  protocols  are  disabled.  When TLS handshakes fail, the
              connection is retried with TLS disabled.  This allows mail delivery to  sites  with
              non-interoperable TLS implementations.

       encrypt
              Mandatory  TLS  encryption.  Since  a  minimum level of security is intended, it is
              reasonable to be specific about sufficiently secure protocol versions and  ciphers.
              At     this     security    level    and    higher,    the    main.cf    parameters
              smtp_tls_mandatory_protocols  and  smtp_tls_mandatory_ciphers   specify   the   TLS
              protocols  and minimum cipher grade which the administrator considers secure enough
              for mandatory encrypted sessions. This security level is not an appropriate default
              for systems delivering mail to the Internet.

       dane   Opportunistic DANE TLS.  At this security level, the TLS policy for the destination
              is obtained via DNSSEC.  For TLSA policy to be in effect, the destination  domain's
              containing  DNS  zone must be signed and the Postfix SMTP client's operating system
              must be configured to send its DNS queries to a recursive DNS  nameserver  that  is
              able  to  validate  the  signed  records.   Each  MX host's DNS zone should also be
              signed, and should publish DANE TLSA (RFC 7672) records that specify  how  that  MX
              host's  TLS  certificate is to be verified.  TLSA records do not preempt the normal
              SMTP MX host selection algorithm, if some MX hosts support TLSA and others do  not,
              TLS  security will vary from delivery to delivery.  It is up to the domain owner to
              configure their MX hosts and their DNS sensibly.  To  configure  the  Postfix  SMTP
              client  for  DNSSEC  lookups  see  the documentation for the smtp_dns_support_level
              main.cf parameter.  When DNSSEC-validated TLSA records are not found the  effective
              tls security level is "may".  When TLSA records are found, but are all unusable the
              effective security level  is  "encrypt".   For  purposes  of  protocol  and  cipher
              selection,  the  "dane"  security  level is treated like a "mandatory" TLS security
              level, and weak ciphers and  protocols  are  disabled.   Since  DANE  authenticates
              server  certificates  the  "aNULL" cipher-suites are transparently excluded at this
              level, no need to configure this manually.  RFC 7672 (DANE) TLS  authentication  is
              available with Postfix 2.11 and later.

       dane-only
              Mandatory  DANE  TLS.  This is just like "dane" above, but DANE TLSA authentication
              is required.  There is no fallback to "may" or  "encrypt"  when  TLSA  records  are
              missing  or unusable.  RFC 7672 (DANE) TLS authentication is available with Postfix
              2.11 and later.

       fingerprint
              Certificate fingerprint verification.  At this security level, there are no trusted
              Certification Authorities.  The certificate trust chain, expiration date, etc., are
              not checked.  Instead,  the  smtp_tls_fingerprint_cert_match  parameter  lists  the
              certificate  fingerprint  or  public key fingerprint (Postfix 2.9 and later) of the
              valid server certificate. The digest algorithm used to calculate the fingerprint is
              selected  by  the smtp_tls_fingerprint_digest parameter. Available with Postfix 2.5
              and later.

       verify Mandatory TLS verification. At this security level, DNS MX lookups are  trusted  to
              be  secure  enough,  and  the  name  verified  in the server certificate is usually
              obtained    indirectly    via    unauthenticated    DNS     MX     lookups.     The
              smtp_tls_verify_cert_match  parameter  controls how the server name is verified. In
              practice explicit control over matching is  more  common  at  the  "secure"  level,
              described  below.  This  security  level  is not an appropriate default for systems
              delivering mail to the Internet.

       secure Secure-channel TLS.  At this security level, DNS  MX  lookups,  though  potentially
              used  to  determine the candidate next-hop gateway IP addresses, are not trusted to
              be secure enough for TLS peername verification. Instead, the default name  verified
              in  the server certificate is obtained from the next-hop domain as specified in the
              smtp_tls_secure_cert_match configuration parameter. The default  matching  rule  is
              that  a  server certificate matches when its name is equal to or is a sub-domain of
              the nexthop domain. This security level is not an appropriate default  for  systems
              delivering mail to the Internet.

       Examples:

       # No TLS. Formerly: smtp_use_tls=no and smtp_enforce_tls=no.
       smtp_tls_security_level = none

       # Opportunistic TLS.
       smtp_tls_security_level = may
       # Postfix >= 2.6:
       # Do not tweak opportunistic ciphers or protocol unless it is essential
       # to do so (if a security vulnerability is found in the SSL library that
       # can be mitigated by disabling a particular protocol or raising the
       # cipher grade from "export" to "low" or "medium").
       smtp_tls_ciphers = export
       smtp_tls_protocols = !SSLv2, !SSLv3

       # Mandatory (high-grade) TLS encryption.
       smtp_tls_security_level = encrypt
       smtp_tls_mandatory_ciphers = high

       # Mandatory TLS verification of hostname or nexthop domain.
       smtp_tls_security_level = verify
       smtp_tls_mandatory_ciphers = high
       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       # Secure channel TLS with exact nexthop name match.
       smtp_tls_security_level = secure
       smtp_tls_mandatory_protocols = TLSv1
       smtp_tls_mandatory_ciphers = high
       smtp_tls_secure_cert_match = nexthop

       # Certificate fingerprint verification (Postfix >= 2.5).
       # The CA-less "fingerprint" security level only scales to a limited
       # number of destinations. As a global default rather than a per-site
       # setting, this is practical when mail for all recipients is sent
       # to a central mail hub.
       relayhost = [mailhub.example.com]
       smtp_tls_security_level = fingerprint
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       smtp_tls_mandatory_ciphers = high
       smtp_tls_fingerprint_cert_match =
           3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
           EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.3 and later.

smtp_tls_session_cache_database (default: empty)

       Name  of the file containing the optional Postfix SMTP client TLS session cache. Specify a
       database type that supports enumeration, such as btree  or  sdbm;  there  is  no  need  to
       support  concurrent  access.  The file is created if it does not exist. The smtp(8) daemon
       does not use this parameter directly, rather the cache is implemented  indirectly  in  the
       tlsmgr(8)  daemon. This means that per-smtp-instance master.cf overrides of this parameter
       are not effective.  Note, that each of the cache databases supported by tlsmgr(8)  daemon:
       $smtpd_tls_session_cache_database,  $smtp_tls_session_cache_database (and with Postfix 2.3
       and later $lmtp_tls_session_cache_database), needs to be stored separately. It is  not  at
       this time possible to store multiple caches in a single database.

       Note: dbm databases are not suitable. TLS session objects are too large.

       As of version 2.5, Postfix no longer uses root privileges when opening this file. The file
       should now be stored under the  Postfix-owned  data_directory.  As  a  migration  aid,  an
       attempt  to open the file under a non-Postfix directory is redirected to the Postfix-owned
       data_directory, and a warning is logged.

       Example:

       smtp_tls_session_cache_database = btree:/var/lib/postfix/smtp_scache

       This feature is available in Postfix 2.2 and later.

smtp_tls_session_cache_timeout (default: 3600s)

       The expiration time of Postfix SMTP client TLS session cache information.  A cache cleanup
       is   performed   periodically   every  $smtp_tls_session_cache_timeout  seconds.  As  with
       $smtp_tls_session_cache_database, this parameter is implemented in  the  tlsmgr(8)  daemon
       and therefore per-smtp-instance master.cf overrides are not possible.

       As  of  Postfix 2.11 this setting cannot exceed 100 days.  If set <= 0, session caching is
       disabled.  If set to a positive value less than 2 minutes, the minimum value of 2  minutes
       is used instead.

       This feature is available in Postfix 2.2 and later.

smtp_tls_trust_anchor_file (default: empty)

       Zero  or  more PEM-format files with trust-anchor certificates and/or public keys.  If the
       parameter is not empty the root CAs in CAfile and CApath are no longer  trusted.   Rather,
       the  Postfix  SMTP  client  will  only  trust  certificate-chains  signed  by  one  of the
       trust-anchors contained in the chosen files.  The specified trust-anchor certificates  and
       public  keys  are not subject to expiration, and need not be (self-signed) root CAs.  They
       may, if desired, be intermediate certificates. Therefore, these certificates also  may  be
       found  "in  the  middle"  of  the trust chain presented by the remote SMTP server, and any
       untrusted issuing parent certificates will  be  ignored.   Specify  a  list  of  pathnames
       separated by comma or whitespace.

       Whether  specified  in  main.cf,  or on a per-destination basis, the trust-anchor PEM file
       must be accessible to the Postfix SMTP client in  the  chroot  jail  if  applicable.   The
       trust-anchor  file  should  contain  only  certificates  and  public  keys, no private key
       material, and must be readable  by  the  non-privileged  $mail_owner  user.   This  allows
       destinations to be bound to a set of specific CAs or public keys without trusting the same
       CAs for all destinations.

       The main.cf parameter supports single-purpose Postfix installations that send  mail  to  a
       fixed  set of SMTP peers.  At most sites, if trust-anchor files are used at all, they will
       be specified on a per-destination basis via the "tafile" attribute  of  the  "verify"  and
       "secure" levels in smtp_tls_policy_maps.

       The  underlying  mechanism is in support of RFC 7672 (DANE TLSA), which defines mechanisms
       for an SMTP client MTA to securely determine server TLS certificates via DNS.

       If you want your trust anchors to be public keys, with OpenSSL you can  extract  a  single
       PEM public key from a PEM X.509 file containing a single certificate, as follows:

           $ openssl x509 -in cert.pem -out ta-key.pem -noout -pubkey

       This feature is available in Postfix 2.11 and later.

smtp_tls_verify_cert_match (default: hostname)

       How  the Postfix SMTP client verifies the server certificate peername for the "verify" TLS
       security level. In a "verify" TLS policy table ($smtp_tls_policy_maps) entry the  optional
       "match" attribute overrides this main.cf setting.

       This  parameter  specifies  one  or  more  patterns  or  strategies  separated  by commas,
       whitespace or colons.  In  the  policy  table  the  only  valid  separator  is  the  colon
       character.

       Patterns specify domain names, or domain name suffixes:

       example.com
              Match  the example.com domain, i.e. one of the names the server certificate must be
              example.com, upper and lower case distinctions are ignored.

       .example.com
              Match subdomains of the example.com  domain,  i.e.  match  a  name  in  the  server
              certificate that consists of a non-zero number of labels followed by a .example.com
              suffix. Case distinctions are ignored.

       Strategies specify a transformation from the next-hop domain to the expected name  in  the
       server certificate:

       nexthop
              Match  against  the  next-hop  domain, which is either the recipient domain, or the
              transport next-hop configured for the domain stripped of any optional  socket  type
              prefix,  enclosing  square  brackets  and  trailing  port.  When MX lookups are not
              suppressed, this is the original nexthop domain prior to the  MX  lookup,  not  the
              result  of  the  MX lookup. For LMTP delivery via UNIX-domain sockets, the verified
              next-hop name is $myhostname.  This strategy is suitable for use with the  "secure"
              policy. Case is ignored.

       dot-nexthop
              As  above,  but  match server certificate names that are subdomains of the next-hop
              domain. Case is ignored.

       hostname
              Match against the hostname of the server, often obtained via an unauthenticated DNS
              MX  lookup.  For  LMTP  delivery  via  UNIX-domain  sockets,  the  verified name is
              $myhostname. This matches the verification strategy of the "MUST"  keyword  in  the
              obsolete  smtp_tls_per_site  table,  and  is  suitable  for  use  with the "verify"
              security level. When the next-hop name is enclosed in square brackets  to  suppress
              MX  lookups, the "hostname" strategy is the same as the "nexthop" strategy. Case is
              ignored.

       Sample main.cf setting:

       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       Sample policy table override:

       example.com     verify  match=hostname:nexthop
       .example.com    verify  match=example.com:.example.com:hostname

       This feature is available in Postfix 2.3 and later.

smtp_tls_wrappermode (default: no)

       Request that the Postfix SMTP client connects using the legacy SMTPS protocol  instead  of
       using the STARTTLS command.

       This mode requires "smtp_tls_security_level = encrypt" or stronger.

       Example: deliver all remote mail via a provider's server "mail.example.com".

       /etc/postfix/main.cf:
           # Client-side SMTPS requires "encrypt" or stronger.
           smtp_tls_security_level = encrypt
           smtp_tls_wrappermode = yes
           # The [] suppress MX lookups.
           relayhost = [mail.example.com]:465

       More examples are in TLS_README, including examples for older Postfix versions.

       This feature is available in Postfix 3.0 and later.

smtp_use_tls (default: no)

       Opportunistic  mode:  use  TLS  when  a  remote  SMTP  server  announces STARTTLS support,
       otherwise send the mail in the clear. Beware: some SMTP servers offer STARTTLS even if  it
       is not configured.  With Postfix < 2.3, if the TLS handshake fails, and no other server is
       available, delivery is deferred and mail stays in the queue. If this is a concern for you,
       use the smtp_tls_per_site feature instead.

       This  feature  is  available  in  Postfix  2.2  and  later. With Postfix 2.3 and later use
       smtp_tls_security_level instead.

smtp_xforward_timeout (default: 300s)

       The Postfix SMTP client time limit for sending the XFORWARD command, and for receiving the
       remote SMTP server response.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_authorized_verp_clients (default: $authorized_verp_clients)

       What remote SMTP clients are allowed to specify the XVERP command.  This command  requests
       that mail be delivered one recipient at a time with a per recipient return address.

       By default, no clients are allowed to specify XVERP.

       This  parameter  was  renamed  with  Postfix  version  2.1. The default value is backwards
       compatible with Postfix version 2.0.

       Specify a list of network/netmask patterns, separated by  commas  and/or  whitespace.  The
       mask  specifies  the  number  of  bits in the network part of a host address. You can also
       specify hostnames or .domain names (the initial dot causes the domain to  match  any  name
       below  it),  "/file/name" or "type:table" patterns.  A "/file/name" pattern is replaced by
       its contents; a "type:table" lookup table is matched when a table entry matches  a  lookup
       string (the lookup result is ignored).  Continue long lines by starting the next line with
       whitespace. Specify "!pattern" to exclude an address or network block from the  list.  The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note:   IP   version   6   address   information  must  be  specified  inside  []  in  the
       smtpd_authorized_verp_clients value, and in files specified with "/file/name".  IP version
       6 addresses contain the ":" character, and would otherwise be confused with a "type:table"
       pattern.

smtpd_authorized_xclient_hosts (default: empty)

       What remote SMTP clients are allowed to use the XCLIENT feature.  This  command  overrides
       remote  SMTP  client  information  that  is  used  for  access control. Typical use is for
       SMTP-based content filters, fetchmail-like programs, or SMTP server access  rule  testing.
       See the XCLIENT_README document for details.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XCLIENT.

       Specify  a  list  of  network/netmask patterns, separated by commas and/or whitespace. The
       mask specifies the number of bits in the network part of a  host  address.  You  can  also
       specify  hostnames  or  .domain names (the initial dot causes the domain to match any name
       below it),  "/file/name" or "type:table" patterns.  A "/file/name" pattern is replaced  by
       its  contents;  a "type:table" lookup table is matched when a table entry matches a lookup
       string (the lookup result is ignored).  Continue long lines by starting the next line with
       whitespace.  Specify  "!pattern" to exclude an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note:  IP  version  6  address  information  must  be   specified   inside   []   in   the
       smtpd_authorized_xclient_hosts  value,  and  in  files  specified  with  "/file/name".  IP
       version 6 addresses contain the ":" character, and would  otherwise  be  confused  with  a
       "type:table" pattern.

smtpd_authorized_xforward_hosts (default: empty)

       What  remote  SMTP clients are allowed to use the XFORWARD feature.  This command forwards
       information that is used to improve logging after  SMTP-based  content  filters.  See  the
       XFORWARD_README document for details.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XFORWARD.

       Specify  a  list  of  network/netmask patterns, separated by commas and/or whitespace. The
       mask specifies the number of bits in the network part of a  host  address.  You  can  also
       specify  hostnames  or  .domain names (the initial dot causes the domain to match any name
       below it),  "/file/name" or "type:table" patterns.  A "/file/name" pattern is replaced  by
       its  contents;  a "type:table" lookup table is matched when a table entry matches a lookup
       string (the lookup result is ignored).  Continue long lines by starting the next line with
       whitespace.  Specify  "!pattern" to exclude an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note:  IP  version  6  address  information  must  be   specified   inside   []   in   the
       smtpd_authorized_xforward_hosts  value,  and  in  files  specified  with "/file/name".  IP
       version 6 addresses contain the ":" character, and would  otherwise  be  confused  with  a
       "type:table" pattern.

smtpd_banner (default: $myhostname ESMTP $mail_name)

       The text that follows the 220 status code in the SMTP greeting banner. Some people like to
       see the mail version advertised. By default, Postfix shows no version.

       You MUST specify $myhostname at the start of the  text.  This  is  required  by  the  SMTP
       protocol.

       Example:

       smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)

smtpd_client_auth_rate_limit (default: 0)

       The maximal number of AUTH commands that any client is allowed to send to this service per
       time unit, regardless of whether or not Postfix actually accepts those commands.  The time
       unit is specified with the anvil_rate_time_unit configuration parameter.

       By default, there is no limit on the number AUTH commands that a client may send.

       To disable this feature, specify a limit of 0.

       WARNING:  The  purpose  of this feature is to limit abuse. It must not be used to regulate
       legitimate mail traffic.

       This feature is available in Postfix 3.1 and later.

smtpd_client_connection_count_limit (default: 50)

       How many simultaneous connections any client is allowed  to  make  to  this  service.   By
       default, the limit is set to half the default process limit value.

       To disable this feature, specify a limit of 0.

       WARNING:  The  purpose  of this feature is to limit abuse. It must not be used to regulate
       legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

smtpd_client_connection_rate_limit (default: 0)

       The maximal number of connection attempts any client is allowed to make  to  this  service
       per  time  unit.   The  time unit is specified with the anvil_rate_time_unit configuration
       parameter.

       By default, a client can make as many connections per time unit as Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not be  used  to  regulate
       legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_connection_rate_limit = 1000

smtpd_client_event_limit_exceptions (default: $mynetworks)

       Clients  that  are  excluded  from  smtpd_client_*_count/rate_limit  restrictions. See the
       mynetworks parameter description for the parameter value syntax.

       By default, clients in trusted networks are excluded. Specify a list  of  network  blocks,
       hostnames or .domain names (the initial dot causes the domain to match any name below it).

       Note:   IP   version   6   address   information  must  be  specified  inside  []  in  the
       smtpd_client_event_limit_exceptions value, and in files specified with  "/file/name".   IP
       version  6  addresses  contain  the  ":" character, and would otherwise be confused with a
       "type:table" pattern.

       Pattern  matching  of  domain  names  is  controlled  by  the  presence  or   absence   of
       "smtpd_client_event_limit_exceptions"  in  the  parent_domain_matches_subdomains parameter
       value (postfix 3.0 and later).

       This feature is available in Postfix 2.2 and later.

smtpd_client_message_rate_limit (default: 0)

       The maximal number of message delivery requests that any client is allowed to make to this
       service  per  time  unit,  regardless  of  whether  or  not Postfix actually accepts those
       messages.   The  time  unit  is  specified  with  the  anvil_rate_time_unit  configuration
       parameter.

       By  default,  a client can send as many message delivery requests per time unit as Postfix
       can accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not be  used  to  regulate
       legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_message_rate_limit = 1000

smtpd_client_new_tls_session_rate_limit (default: 0)

       The  maximal  number  of  new  (i.e.,  uncached) TLS sessions that a remote SMTP client is
       allowed to negotiate with this service per time unit.  The time unit is specified with the
       anvil_rate_time_unit configuration parameter.

       By  default,  a remote SMTP client can negotiate as many new TLS sessions per time unit as
       Postfix can accept.

       To disable this feature, specify a limit of 0. Otherwise, specify a limit that is at least
       the  per-client  concurrent  session  limit,  or  else  legitimate  client sessions may be
       rejected.

       WARNING: The purpose of this feature is to limit abuse. It must not be  used  to  regulate
       legitimate mail traffic.

       This feature is available in Postfix 2.3 and later.

       Example:

       smtpd_client_new_tls_session_rate_limit = 100

smtpd_client_port_logging (default: no)

       Enable  logging of the remote SMTP client port in addition to the hostname and IP address.
       The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

smtpd_client_recipient_rate_limit (default: 0)

       The maximal number of recipient addresses that any client  is  allowed  to  send  to  this
       service  per  time  unit,  regardless  of  whether  or  not Postfix actually accepts those
       recipients.  The time  unit  is  specified  with  the  anvil_rate_time_unit  configuration
       parameter.

       By  default,  a  client  can send as many recipient addresses per time unit as Postfix can
       accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not be  used  to  regulate
       legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_recipient_rate_limit = 1000

smtpd_client_restrictions (default: empty)

       Optional  restrictions  that  the  Postfix  SMTP server applies in the context of a client
       connection request.  See SMTPD_ACCESS_README, section "Delayed evaluation of  SMTP  access
       restriction lists" for a discussion of evaluation context and time.

       The default is to allow all connection requests.

       Specify  a  list  of  restrictions,  separated by commas and/or whitespace.  Continue long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The  following  restrictions  are  specific  to  client hostname or client network address
       information.

       check_ccert_access type:table
              Use the remote SMTP client certificate fingerprint or the  public  key  fingerprint
              (Postfix  2.9  and  later) as lookup key for the specified access(5) database; with
              Postfix version 2.2, also require  that  the  remote  SMTP  client  certificate  is
              verified  successfully.   The  fingerprint digest algorithm is configurable via the
              smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to Postfix  version
              2.5).  This feature is available with Postfix version 2.2 and later.

       check_client_access type:table
              Search  the  specified  access  database  for  the client hostname, parent domains,
              client IP address, or networks obtained by stripping least significant octets.  See
              the access(5) manual page for details.

       check_client_a_access type:table
              Search  the  specified  access(5)  database  for  the  IP  addresses for the client
              hostname, and execute the corresponding action.  Note: a  result  of  "OK"  is  not
              allowed  for  safety reasons. Instead, use DUNNO in order to exclude specific hosts
              from blacklists.  This feature is available in Postfix 3.0 and later.

       check_client_mx_access type:table
              Search the specified access(5) database for the MX hosts for the  client  hostname,
              and  execute  the  corresponding action.  Note: a result of "OK" is not allowed for
              safety reasons. Instead,  use  DUNNO  in  order  to  exclude  specific  hosts  from
              blacklists.  This feature is available in Postfix 2.7 and later.

       check_client_ns_access type:table
              Search  the  specified  access(5)  database  for  the  DNS  servers  for the client
              hostname, and execute the corresponding action.  Note: a  result  of  "OK"  is  not
              allowed  for  safety reasons. Instead, use DUNNO in order to exclude specific hosts
              from blacklists.  This feature is available in Postfix 2.7 and later.

       check_reverse_client_hostname_access type:table
              Search the specified access database for the unverified  reverse  client  hostname,
              parent  domains,  client  IP  address,  or  networks  obtained  by  stripping least
              significant octets. See the access(5) manual page for details.  Note: a  result  of
              "OK"  is  not  allowed  for safety reasons.  Instead, use DUNNO in order to exclude
              specific hosts from blacklists.  This feature  is  available  in  Postfix  2.6  and
              later.

       check_reverse_client_hostname_a_access type:table
              Search  the  specified  access(5)  database for the IP addresses for the unverified
              reverse client hostname, and execute the corresponding action.  Note: a  result  of
              "OK"  is  not  allowed  for safety reasons.  Instead, use DUNNO in order to exclude
              specific hosts from blacklists.  This feature  is  available  in  Postfix  3.0  and
              later.

       check_reverse_client_hostname_mx_access type:table
              Search the specified access(5) database for the MX hosts for the unverified reverse
              client hostname, and execute the corresponding action.  Note: a result of  "OK"  is
              not  allowed  for  safety reasons.  Instead, use DUNNO in order to exclude specific
              hosts from blacklists.  This feature is available in Postfix 2.7 and later.

       check_reverse_client_hostname_ns_access type:table
              Search the specified access(5) database for the  DNS  servers  for  the  unverified
              reverse  client  hostname, and execute the corresponding action.  Note: a result of
              "OK" is not allowed for safety reasons.  Instead, use DUNNO  in  order  to  exclude
              specific  hosts  from  blacklists.   This  feature  is available in Postfix 2.7 and
              later.

       check_sasl_access type:table
              Use the remote SMTP client SASL user name as lookup key for the specified access(5)
              database.   The   lookup   key   has   the   form  "username@domainname"  when  the
              smtpd_sasl_local_domain    parameter    value    is    non-empty.     Unlike    the
              check_client_access  feature,  check_sasl_access does not perform matches of parent
              domains or IP subnet ranges.  This feature is available with Postfix  version  2.11
              and later.

       permit_inet_interfaces
              Permit the request when the client IP address matches $inet_interfaces.

       permit_mynetworks
              Permit  the  request  when  the  client  IP  address matches any network or network
              address listed in  $mynetworks.

       permit_sasl_authenticated
              Permit the request when the client is successfully authenticated via the  RFC  4954
              (AUTH) protocol.

       permit_tls_all_clientcerts
              Permit   the   request   when  the  remote  SMTP  client  certificate  is  verified
              successfully.   This  option  must  be  used  only  if  a  special  CA  issues  the
              certificates  and  only  this CA is listed as trusted CA. Otherwise, clients with a
              third-party   certificate   would   also   be   allowed    to    relay.     Specify
              "tls_append_default_CA = no" when the trusted CA is specified with smtpd_tls_CAfile
              or smtpd_tls_CApath, to prevent Postfix from appending the system-supplied  default
              CAs.  This feature is available with Postfix version 2.2.

       permit_tls_clientcerts
              Permit  the  request  when the remote SMTP client certificate fingerprint or public
              key fingerprint (Postfix 2.9 and  later)  is  listed  in  $relay_clientcerts.   The
              fingerprint  digest  algorithm is configurable via the smtpd_tls_fingerprint_digest
              parameter (hard-coded as md5 prior  to  Postfix  version  2.5).   This  feature  is
              available with Postfix version 2.2.

       reject_rbl_client rbl_domain=d.d.d.d
              Reject  the  request  when the reversed client network address is listed with the A
              record "d.d.d.d" under rbl_domain (Postfix version 2.1 and later only).   Each  "d"
              is  a  number,  or  a  pattern  inside "[]" that contains one or more ";"-separated
              numbers or number..number ranges (Postfix version 2.8 and later).  If no "=d.d.d.d"
              is specified, reject the request when the reversed client network address is listed
              with any A record under rbl_domain.
              The  maps_rbl_reject_code  parameter  specifies  the  response  code  for  rejected
              requests  (default:   554),  the default_rbl_reply  parameter specifies the default
              server reply, and  the  rbl_reply_maps   parameter  specifies  tables  with  server
              replies indexed by rbl_domain.  This feature is available in Postfix 2.0 and later.

       permit_dnswl_client dnswl_domain=d.d.d.d
              Accept  the  request  when the reversed client network address is listed with the A
              record "d.d.d.d" under dnswl_domain.  Each "d" is a number,  or  a  pattern  inside
              "[]"  that contains one or more ";"-separated numbers or number..number ranges.  If
              no "=d.d.d.d" is specified, accept the request when  the  reversed  client  network
              address is listed with any A record under dnswl_domain.
              For  safety,  permit_dnswl_client  is  silently  ignored  when  it  would  override
              reject_unauth_destination.  The result is  DEFER_IF_REJECT  when  whitelist  lookup
              fails.  This feature is available in Postfix 2.8 and later.

       reject_rhsbl_client rbl_domain=d.d.d.d
              Reject  the  request when the client hostname is listed with the A record "d.d.d.d"
              under rbl_domain (Postfix version 2.1 and later only).  Each "d" is a number, or  a
              pattern   inside   "[]"   that  contains  one  or  more  ";"-separated  numbers  or
              number..number ranges (Postfix  version  2.8  and  later).   If  no  "=d.d.d.d"  is
              specified,  reject the request when the client hostname is listed with any A record
              under rbl_domain. See the reject_rbl_client description above  for  additional  RBL
              related  configuration  parameters.   This  feature is available in Postfix 2.0 and
              later; with Postfix version 2.8 and later, reject_rhsbl_reverse_client will usually
              produce better results.

       permit_rhswl_client rhswl_domain=d.d.d.d
              Accept  the  request when the client hostname is listed with the A record "d.d.d.d"
              under rhswl_domain.  Each "d" is a number, or a pattern inside "[]"  that  contains
              one  or  more  ";"-separated  numbers or number..number ranges. If no "=d.d.d.d" is
              specified, accept the request when the client hostname is listed with any A  record
              under rhswl_domain.
              Caution: client name whitelisting is fragile, since the client name lookup can fail
              due to temporary outages.  Client name whitelisting should be used only  to  reduce
              false  positives  in  e.g.   DNS-based  blocklists,  and not for making access rule
              exceptions.
              For  safety,  permit_rhswl_client  is  silently  ignored  when  it  would  override
              reject_unauth_destination.   The  result  is  DEFER_IF_REJECT when whitelist lookup
              fails.  This feature is available in Postfix 2.8 and later.

       reject_rhsbl_reverse_client rbl_domain=d.d.d.d
              Reject the request when the unverified reverse client hostname is listed with the A
              record  "d.d.d.d" under rbl_domain.  Each "d" is a number, or a pattern inside "[]"
              that contains one or more ";"-separated numbers or number..number  ranges.   If  no
              "=d.d.d.d"  is  specified,  reject  the  request when the unverified reverse client
              hostname is listed with any A record under rbl_domain.  See  the  reject_rbl_client
              description  above  for  additional  RBL  related  configuration  parameters.  This
              feature is available in Postfix 2.8 and later.

       reject_unknown_client_hostname (with Postfix < 2.3: reject_unknown_client)
              Reject the request when 1) the  client  IP  address->name  mapping  fails,  2)  the
              name->address  mapping  fails,  or  3) the name->address mapping does not match the
              client IP address.
              This is a  stronger  restriction  than  the  reject_unknown_reverse_client_hostname
              feature, which triggers only under condition 1) above.
              The  unknown_client_reject_code  parameter specifies the response code for rejected
              requests (default: 450). The reply is always  450  in  case  the  address->name  or
              name->address lookup failed due to a temporary problem.

       reject_unknown_reverse_client_hostname
              Reject the request when the client IP address has no address->name mapping.
              This is a weaker restriction than the reject_unknown_client_hostname feature, which
              requires not only that the address->name and name->address mappings exist, but also
              that the two mappings reproduce the client IP address.
              The  unknown_client_reject_code  parameter specifies the response code for rejected
              requests (default: 450).  The reply is always 450 in case the address->name  lookup
              failed due to a temporary problem.
              This feature is available in Postfix 2.3 and later.

       In  addition,  you  can use any of the following generic restrictions.  These restrictions
       are applicable in any SMTP command context.

       check_policy_service servername
              Query the  specified  policy  server.  See  the  SMTPD_POLICY_README  document  for
              details. This feature is available in Postfix 2.1 and later.

       defer  Defer  the  request.  The  client  is  told to try again later. This restriction is
              useful at the end of a restriction list, to make the default policy explicit.
              The defer_code parameter specifies the SMTP server reply code (default: 450).

       defer_if_permit
              Defer the request if some later restriction would result in an explicit or implicit
              PERMIT action.  This is useful when a blacklisting feature fails due to a temporary
              problem.  This feature is available in Postfix version 2.1 and later.

       defer_if_reject
              Defer the request if some later restriction would result in a REJECT action.   This
              is  useful  when  a  whitelisting  feature  fails due to a temporary problem.  This
              feature is available in Postfix version 2.1 and later.

       permit Permit the request. This restriction is useful at the end of a restriction list, to
              make the default policy explicit.

       reject_multi_recipient_bounce
              Reject  the  request  when the envelope sender is the null address, and the message
              has multiple envelope recipients. This usage has rare but legitimate  applications:
              under  certain conditions, multi-recipient mail that was posted with the DSN option
              NOTIFY=NEVER may be forwarded with the null sender address.
              Note: this restriction can only work reliably when used in  smtpd_data_restrictions
              or  smtpd_end_of_data_restrictions,  because  the total number of recipients is not
              known at an earlier stage of the SMTP conversation.  Use at  the  RCPT  stage  will
              only reject the second etc.  recipient.
              The  multi_recipient_bounce_reject_code  parameter  specifies the response code for
              rejected requests (default:  550).  This feature is available in  Postfix  2.1  and
              later.

       reject_plaintext_session
              Reject  the  request  when the connection is not encrypted. This restriction should
              not be used before the client has had a chance to  negotiate  encryption  with  the
              AUTH or STARTTLS commands.
              The  plaintext_reject_code  parameter  specifies  the  response  code  for rejected
              requests (default:  450).  This feature is available in Postfix 2.3 and later.

       reject_unauth_pipelining
              Reject the request when the client sends SMTP commands ahead of time  where  it  is
              not  allowed,  or when the client sends SMTP commands ahead of time without knowing
              that Postfix actually supports ESMTP command pipelining. This stops mail from  bulk
              mail  software  that  improperly uses ESMTP command pipelining in order to speed up
              deliveries.
              With Postfix 2.6 and later, the SMTP server sets a  per-session  flag  whenever  it
              detects  illegal  pipelining,  including  pipelined  HELO  or  EHLO  commands.  The
              reject_unauth_pipelining feature simply tests whether the flag was set at any point
              in time during the session.
              With  older Postfix versions, reject_unauth_pipelining checks the current status of
              the input read queue, and its usage is  not  recommended  in  contexts  other  than
              smtpd_data_restrictions.

       reject Reject the request. This restriction is useful at the end of a restriction list, to
              make  the  default  policy  explicit.   The  reject_code  configuration   parameter
              specifies the response code for rejected requests (default: 554).

       sleep seconds
              Pause  for the specified number of seconds and proceed with the next restriction in
              the list, if any. This may stop zombie mail when used as:
              /etc/postfix/main.cf:
                  smtpd_client_restrictions =
                      sleep 1, reject_unauth_pipelining
                  smtpd_delay_reject = no
              This feature is available in Postfix 2.3.

       warn_if_reject
              A safety net for testing. When "warn_if_reject"  is  placed  before  a  reject-type
              restriction,  access  table  query,  or  check_policy_service  query,  this  logs a
              "reject_warning" message  instead  of  rejecting  a  request  (when  a  reject-type
              restriction  fails  due  to a temporary error, this logs a "reject_warning" message
              for any implicit "defer_if_permit" actions that would normally  prevent  mail  from
              being  accepted  by  some  later access restriction). This feature has no effect on
              defer_if_reject restrictions.

       Other restrictions that are valid in this context:

       ·      SMTP   command   specific   restrictions   that    are    described    under    the
              smtpd_helo_restrictions,  smtpd_sender_restrictions or smtpd_recipient_restrictions
              parameters.  When  helo,  sender  or  recipient  restrictions  are   listed   under
              smtpd_client_restrictions,  they  have effect only with "smtpd_delay_reject = yes",
              so that $smtpd_client_restrictions is evaluated at the time of the RCPT TO command.

       Example:

       smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname

smtpd_command_filter (default: empty)

       A mechanism to transform commands from remote SMTP clients.  This is a last-resort tool to
       work  around  client  commands  that  break interoperability with the Postfix SMTP server.
       Other uses involve fault injection to test Postfix's handling of invalid commands.

       Specify the name of a "type:table" lookup table. The search string is the SMTP command  as
       received  from  the  remote  SMTP  client, except that initial whitespace and the trailing
       <CR><LF> are removed.  The result value is executed by the Postfix SMTP server.

       There is no need to use smtpd_command_filter for the following cases:

       ·      Use "resolve_numeric_domain = yes" to accept "user@ipaddress".

       ·      Postfix already accepts the correct form "user@[ipaddress]". Use virtual_alias_maps
              or canonical_maps to translate these into domain names if necessary.

       ·      Use    "strict_rfc821_envelopes    =    no"   to   accept   "RCPT   TO:<User   Name
              <user@example.com>>". Postfix will ignore the "User Name" part and deliver  to  the
              <user@example.com> address.

       Examples of problems that can be solved with the smtpd_command_filter feature:

       /etc/postfix/main.cf:
           smtpd_command_filter = pcre:/etc/postfix/command_filter

       /etc/postfix/command_filter:
           # Work around clients that send malformed HELO commands.
           /^HELO\s*$/ HELO domain.invalid

           # Work around clients that send empty lines.
           /^\s*$/     NOOP

           # Work around clients that send RCPT TO:<'user@domain'>.
           # WARNING: do not lose the parameters that follow the address.
           /^(RCPT\s+TO:\s*<)'([^[:space:]]+)'(>.*)/     $1$2$3

           # Append XVERP to MAIL FROM commands to request VERP-style delivery.
           # See VERP_README for more information on how to use Postfix VERP.
           /^(MAIL FROM:\s*<listname@example\.com>.*)/   $1 XVERP

           # Bounce-never mail sink. Use notify_classes=bounce,resource,software
           # to send bounced mail to the postmaster (with message body removed).
           /^(RCPT\s+TO:\s*<.*>.*)\s+NOTIFY=\S+(.*)/     $1 NOTIFY=NEVER$2
           /^(RCPT\s+TO:.*)/                             $1 NOTIFY=NEVER

       This feature is available in Postfix 2.7.

smtpd_data_restrictions (default: empty)

       Optional  access  restrictions  that the Postfix SMTP server applies in the context of the
       SMTP DATA command.  See SMTPD_ACCESS_README, section "Delayed evaluation  of  SMTP  access
       restriction lists" for a discussion of evaluation context and time.

       This feature is available in Postfix 2.0 and later.

       Specify  a  list  of  restrictions,  separated by commas and/or whitespace.  Continue long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The following restrictions are valid in this context:

       ·      Generic  restrictions that can be used in any SMTP command context, described under
              smtpd_client_restrictions.

       ·      SMTP  command  specific  restrictions  described  under  smtpd_client_restrictions,
              smtpd_helo_restrictions, smtpd_sender_restrictions or smtpd_recipient_restrictions.

       ·      However, no recipient information is available in the case of multi-recipient mail.
              Acting on only one recipient would be misleading, because any decision will  affect
              all  recipients  equally.  Acting  on  all recipients would require a possibly very
              large amount of memory, and would also be  misleading  for  the  reasons  mentioned
              before.

       Examples:

       smtpd_data_restrictions = reject_unauth_pipelining
       smtpd_data_restrictions = reject_multi_recipient_bounce

smtpd_delay_open_until_valid_rcpt (default: yes)

       Postpone  the start of an SMTP mail transaction until a valid RCPT TO command is received.
       Specify "no" to create a mail transaction as soon as the Postfix SMTP  server  receives  a
       valid MAIL FROM command.

       With  sites that reject lots of mail, the default setting reduces the use of disk, CPU and
       memory resources. The downside is that rejected recipients are logged with NOQUEUE instead
       of a mail transaction ID. This complicates the logfile analysis of multi-recipient mail.

       This feature is available in Postfix 2.3 and later.

smtpd_delay_reject (default: yes)

       Wait   until   the   RCPT   TO   command   before  evaluating  $smtpd_client_restrictions,
       $smtpd_helo_restrictions and $smtpd_sender_restrictions, or wait until  the  ETRN  command
       before evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions.

       This  feature  is turned on by default because some clients apparently mis-behave when the
       Postfix SMTP server rejects commands before RCPT TO.

       The default setting has one major benefit: it allows  Postfix  to  log  recipient  address
       information when rejecting a client name/address or sender address, so that it is possible
       to find out whose mail is being rejected.

smtpd_discard_ehlo_keyword_address_maps (default: empty)

       Lookup tables, indexed by the remote SMTP client address, with case insensitive  lists  of
       EHLO  keywords  (pipelining,  starttls,  auth, etc.) that the Postfix SMTP server will not
       send in the EHLO response to a remote SMTP  client.  See  smtpd_discard_ehlo_keywords  for
       details.  The tables are not searched by hostname for robustness reasons.

       Specify  zero  or more "type:name" lookup tables, separated by whitespace or comma. Tables
       will be searched in the specified order until a match is found.

       This feature is available in Postfix 2.2 and later.

smtpd_discard_ehlo_keywords (default: empty)

       A case insensitive list of EHLO keywords  (pipelining,  starttls,  auth,  etc.)  that  the
       Postfix SMTP server will not send in the EHLO response to a remote SMTP client.

       This feature is available in Postfix 2.2 and later.

       Notes:

       ·      Specify the silent-discard pseudo keyword to prevent this action from being logged.

       ·      Use  the  smtpd_discard_ehlo_keyword_address_maps  feature to discard EHLO keywords
              selectively.

smtpd_dns_reply_filter (default: empty)

       Optional filter for Postfix SMTP server DNS lookup results.  See smtp_dns_reply_filter for
       details including an example.

       This feature is available in Postfix 3.0 and later.

smtpd_end_of_data_restrictions (default: empty)

       Optional  access  restrictions  that the Postfix SMTP server applies in the context of the
       SMTP END-OF-DATA command.  See SMTPD_ACCESS_README, section "Delayed  evaluation  of  SMTP
       access restriction lists" for a discussion of evaluation context and time.

       This feature is available in Postfix 2.2 and later.

       See smtpd_data_restrictions for details and limitations.

smtpd_enforce_tls (default: no)

       Mandatory  TLS: announce STARTTLS support to remote SMTP clients, and require that clients
       use TLS encryption.  According to RFC  2487  this  MUST  NOT  be  applied  in  case  of  a
       publicly-referenced SMTP server.  This option is therefore off by default.

       Note 1: "smtpd_enforce_tls = yes" implies "smtpd_tls_auth_only = yes".

       Note  2:  when  invoked  via  "sendmail  -bs",  Postfix  will  never offer STARTTLS due to
       insufficient privileges to access the server private key. This is intended behavior.

       This feature is available in Postfix 2.2  and  later.  With  Postfix  2.3  and  later  use
       smtpd_tls_security_level instead.

smtpd_error_sleep_time (default: 1s)

       With Postfix version 2.1 and later: the SMTP server response delay after a client has made
       more than $smtpd_soft_error_limit errors, and fewer than  $smtpd_hard_error_limit  errors,
       without delivering mail.

       With  Postfix  version 2.0 and earlier: the SMTP server delay before sending a reject (4xx
       or 5xx) response, when the client  has  made  fewer  than  $smtpd_soft_error_limit  errors
       without delivering mail.

smtpd_etrn_restrictions (default: empty)

       Optional restrictions that the Postfix SMTP server applies in the context of a client ETRN
       command.  See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access  restriction
       lists" for a discussion of evaluation context and time.

       The  Postfix  ETRN  implementation  accepts  only  destinations  that are eligible for the
       Postfix "fast flush" service. See the ETRN_README file for details.

       Specify a list of restrictions, separated by  commas  and/or  whitespace.   Continue  long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The following restrictions are specific to the domain name information received  with  the
       ETRN command.

       check_etrn_access type:table
              Search  the  specified  access  database  for  the  ETRN  domain name or its parent
              domains. See the access(5) manual page for details.

       Other restrictions that are valid in this context:

       ·      Generic restrictions that can be used in any SMTP command context, described  under
              smtpd_client_restrictions.

       ·      SMTP  command  specific  restrictions described under smtpd_client_restrictions and
              smtpd_helo_restrictions.

       Example:

       smtpd_etrn_restrictions = permit_mynetworks, reject

smtpd_expansion_filter (default: see postconf -d output)

       What characters are allowed in $name expansions of RBL reply templates. Characters not  in
       the  allowed  set  are  replaced by "_".  Use C like escapes to specify special characters
       such as whitespace.

       This parameter is not subjected to $parameter expansion.

       This feature is available in Postfix 2.0 and later.

smtpd_forbidden_commands (default: CONNECT, GET, POST)

       List of commands that cause the Postfix SMTP server to immediately terminate  the  session
       with  a  221  code. This can be used to disconnect clients that obviously attempt to abuse
       the system. In addition to the commands listed in this parameter, commands that follow the
       "Label:" format of message headers will also cause a disconnect.

       This feature is available in Postfix 2.2 and later.

smtpd_hard_error_limit (default: normal: 20, overload: 1)

       The  maximal  number  of errors a remote SMTP client is allowed to make without delivering
       mail. The Postfix SMTP server disconnects when the limit is exceeded. Normally the default
       limit  is  20,  but it changes under overload to just 1. With Postfix 2.5 and earlier, the
       SMTP server always allows up to 20 errors by default.

smtpd_helo_required (default: no)

       Require that a remote SMTP client introduces itself with the HELO or EHLO  command  before
       sending the MAIL command or other commands that require EHLO negotiation.

       Example:

       smtpd_helo_required = yes

smtpd_helo_restrictions (default: empty)

       Optional restrictions that the Postfix SMTP server applies in the context of a client HELO
       command.  See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access  restriction
       lists" for a discussion of evaluation context and time.

       The default is to permit everything.

       Note:  specify  "smtpd_helo_required  =  yes"  to  fully enforce this restriction (without
       "smtpd_helo_required = yes", a client  can  simply  skip  smtpd_helo_restrictions  by  not
       sending HELO or EHLO).

       Specify  a  list  of  restrictions,  separated by commas and/or whitespace.  Continue long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The following restrictions are specific to the hostname information received with the HELO
       or EHLO command.

       check_helo_access type:table
              Search the specified access(5) database for the HELO or  EHLO  hostname  or  parent
              domains,  and execute the corresponding action.  Note: specify "smtpd_helo_required
              = yes" to fully enforce this restriction (without "smtpd_helo_required  =  yes",  a
              client can simply skip check_helo_access by not sending HELO or EHLO).

       check_helo_a_access type:table
              Search  the  specified access(5) database for the IP addresses for the HELO or EHLO
              hostname, and execute the corresponding action.  Note 1: a result of  "OK"  is  not
              allowed  for  safety reasons. Instead, use DUNNO in order to exclude specific hosts
              from blacklists.  Note 2: specify "smtpd_helo_required = yes" to fully enforce this
              restriction  (without  "smtpd_helo_required  =  yes",  a  client  can  simply  skip
              check_helo_a_access by not sending HELO or EHLO).  This  feature  is  available  in
              Postfix 3.0 and later.

       check_helo_mx_access type:table
              Search  the  specified  access(5)  database  for  the MX hosts for the HELO or EHLO
              hostname, and execute the corresponding action.  Note 1: a result of  "OK"  is  not
              allowed  for  safety reasons. Instead, use DUNNO in order to exclude specific hosts
              from blacklists.  Note 2: specify "smtpd_helo_required = yes" to fully enforce this
              restriction  (without  "smtpd_helo_required  =  yes",  a  client  can  simply  skip
              check_helo_mx_access by not sending HELO or EHLO).  This feature  is  available  in
              Postfix 2.1 and later.

       check_helo_ns_access type:table
              Search  the  specified  access(5) database for the DNS servers for the HELO or EHLO
              hostname, and execute the corresponding action.  Note 1: a result of  "OK"  is  not
              allowed  for  safety reasons. Instead, use DUNNO in order to exclude specific hosts
              from blacklists.  Note 2: specify "smtpd_helo_required = yes" to fully enforce this
              restriction  (without  "smtpd_helo_required  =  yes",  a  client  can  simply  skip
              check_helo_ns_access by not sending HELO or EHLO). This  feature  is  available  in
              Postfix 2.1 and later.

       reject_invalid_helo_hostname (with Postfix < 2.3: reject_invalid_hostname)
              Reject  the  request  when  the  HELO or EHLO hostname is malformed.  Note: specify
              "smtpd_helo_required  =  yes"  to   fully   enforce   this   restriction   (without
              "smtpd_helo_required  = yes", a client can simply skip reject_invalid_helo_hostname
              by not sending HELO or EHLO).
              The invalid_hostname_reject_code specifies the response code for rejected  requests
              (default: 501).

       reject_non_fqdn_helo_hostname (with Postfix < 2.3: reject_non_fqdn_hostname)
              Reject  the request when the HELO or EHLO hostname is not in fully-qualified domain
              or address literal form, as required by the RFC. Note: specify "smtpd_helo_required
              =  yes"  to  fully enforce this restriction (without "smtpd_helo_required = yes", a
              client can simply skip reject_non_fqdn_helo_hostname by not sending HELO or EHLO).
              The  non_fqdn_reject_code  parameter  specifies  the  response  code  for  rejected
              requests (default: 504).

       reject_rhsbl_helo rbl_domain=d.d.d.d
              Reject  the  request  when  the  HELO  or EHLO hostname is listed with the A record
              "d.d.d.d" under rbl_domain (Postfix version 2.1 and later only).   Each  "d"  is  a
              number, or a pattern inside "[]" that contains one or more ";"-separated numbers or
              number..number ranges (Postfix  version  2.8  and  later).   If  no  "=d.d.d.d"  is
              specified,  reject  the request when the HELO or EHLO hostname is listed with any A
              record under rbl_domain. See the reject_rbl_client description for  additional  RBL
              related  configuration  parameters.   Note:  specify "smtpd_helo_required = yes" to
              fully enforce this restriction (without "smtpd_helo_required = yes", a  client  can
              simply  skip  reject_rhsbl_helo  by  not  sending  HELO  or  EHLO). This feature is
              available in Postfix 2.0 and later.

       reject_unknown_helo_hostname (with Postfix < 2.3: reject_unknown_hostname)
              Reject the request when the HELO or EHLO hostname has no DNS A or MX record.
              The reply is specified with the  unknown_hostname_reject_code  parameter  (default:
              450)  or unknown_helo_hostname_tempfail_action (default: defer_if_permit).  See the
              respective parameter descriptions for details.
              Note: specify  "smtpd_helo_required  =  yes"  to  fully  enforce  this  restriction
              (without    "smtpd_helo_required    =    yes",    a    client   can   simply   skip
              reject_unknown_helo_hostname by not sending HELO or EHLO).

       Other restrictions that are valid in this context:

       ·      Generic restrictions that can be used in any SMTP command context, described  under
              smtpd_client_restrictions.

       ·      Client   hostname   or   network  address  specific  restrictions  described  under
              smtpd_client_restrictions.

       ·      SMTP command specific restrictions  described  under  smtpd_sender_restrictions  or
              smtpd_recipient_restrictions.   When  sender  or  recipient restrictions are listed
              under smtpd_helo_restrictions, they have effect  only  with  "smtpd_delay_reject  =
              yes",  so  that  $smtpd_helo_restrictions  is  evaluated at the time of the RCPT TO
              command.

       Examples:

       smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname
       smtpd_helo_restrictions = permit_mynetworks, reject_unknown_helo_hostname

smtpd_history_flush_threshold (default: 100)

       The maximal number of lines in the Postfix  SMTP  server  command  history  before  it  is
       flushed upon receipt of EHLO, RSET, or end of DATA.

smtpd_junk_command_limit (default: normal: 100, overload: 1)

       The  number of junk commands (NOOP, VRFY, ETRN or RSET) that a remote SMTP client can send
       before the Postfix SMTP server starts to  increment  the  error  counter  with  each  junk
       command.   The  junk  command  count  is  reset  after  mail  is  delivered.  See also the
       smtpd_error_sleep_time and smtpd_soft_error_limit configuration parameters.  Normally  the
       default  limit  is  100,  but  it  changes  under overload to just 1. With Postfix 2.5 and
       earlier, the SMTP server always allows up to 100 junk commands by default.

smtpd_log_access_permit_actions (default: empty)

       Enable logging of the named "permit" actions in SMTP server access lists (by default,  the
       SMTP server logs "reject" actions but not "permit" actions).  This feature does not affect
       conditional actions such as "defer_if_permit".

       Specify a list of "permit" action names, "/file/name" or "type:table" patterns,  separated
       by  commas  and/or  whitespace. The list is matched left to right, and the search stops on
       the first match. A "/file/name" pattern is replaced by its contents; a "type:table" lookup
       table  is  matched  when  a  name  matches  a  lookup  key (the lookup result is ignored).
       Continue long lines by starting the next  line  with  whitespace.  Specify  "!pattern"  to
       exclude a name from the list.

       Examples:

       /etc/postfix/main.cf:
           # Log all "permit" actions.
           smtpd_log_access_permit_actions = static:all

       /etc/postfix/main.cf:
           # Log "permit_dnswl_client" only.
           smtpd_log_access_permit_actions = permit_dnswl_client

       This feature is available in Postfix 2.10 and later.

smtpd_milter_maps (default: empty)

       Lookup  tables  with Milter settings per remote SMTP client IP address.  The lookup result
       overrides the smtpd_milters setting, and has the same syntax.

       Note: lookup tables cannot return empty responses. Specify  a  lookup  result  of  DISABLE
       (case does not matter) to indicate that Milter support should be disabled.

       Example to disable Milters for local clients:

       /etc/postfix/main.cf:
           smtpd_milter_maps = cidr:/etc/postfix/smtpd_milter_map
           smtpd_milters = inet:host:port, { inet:host:port, ... }, ...

       /etc/postfix/smtpd_milter_map:
           # Disable Milters for local clients.
           127.0.0.0/8    DISABLE
           192.168.0.0/16 DISABLE
           ::/64          DISABLE
           2001:db8::/32  DISABLE

       This feature is available in Postfix 3.2 and later.

smtpd_milters (default: empty)

       A  list  of  Milter  (mail  filter) applications for new mail that arrives via the Postfix
       smtpd(8) server. Specify space or comma as separator. See the MILTER_README  document  for
       details.

       This feature is available in Postfix 2.3 and later.

smtpd_noop_commands (default: empty)

       List  of commands that the Postfix SMTP server replies to with "250 Ok", without doing any
       syntax checks and without changing state.  This list overrides any commands built into the
       Postfix SMTP server.

smtpd_null_access_lookup_key (default: <>)

       The lookup key to be used in SMTP access(5) tables instead of the null sender address.

smtpd_peername_lookup (default: yes)

       Attempt  to  look up the remote SMTP client hostname, and verify that the name matches the
       client IP address. A client name is set to "unknown"  when  it  cannot  be  looked  up  or
       verified,  or when name lookup is disabled.  Turning off name lookup reduces delays due to
       DNS lookup and increases the maximal inbound delivery rate.

       This feature is available in Postfix 2.3 and later.

smtpd_per_record_deadline (default: normal: no, overload: yes)

       Change the behavior of the smtpd_timeout and smtpd_starttls_timeout time  limits,  from  a
       time  limit  per  read or write system call, to a time limit to send or receive a complete
       record (an SMTP command line, SMTP response  line,  SMTP  message  content  line,  or  TLS
       protocol  message).   This limits the impact from hostile peers that trickle data one byte
       at a time.

       Note: when per-record deadlines are enabled, a short timeout may cause problems  with  TLS
       over very slow network connections.  The reasons are that a TLS protocol message can be up
       to 16 kbytes long (with TLSv1), and that an entire TLS protocol message must  be  sent  or
       received within the per-record deadline.

       This  feature  is  available  in  Postfix  2.9 and later. With older Postfix releases, the
       behavior is as if this parameter is set to "no".

smtpd_policy_service_default_action (default: 451 4.3.5 Server configuration problem)

       The default action when an SMTPD policy service request fails.  Specify "DUNNO" to  behave
       as  if  the  failed  SMTPD policy service request was not sent, and to continue processing
       other access restrictions, if any.

       Limitations:

       ·      This parameter may specify any value that would be  a  valid  SMTPD  policy  server
              response  (or  access(5)  map lookup result).  An access(5) map or policy server in
              this parameter value may need to be declared in advance  with  a  restriction_class
              setting.

       ·      If  the specified action invokes another check_policy_service request, that request
              will have the built-in default action.

       This feature is available in Postfix 3.0 and later.

smtpd_policy_service_max_idle (default: 300s)

       The time after which an idle SMTPD policy service connection is closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_max_ttl (default: 1000s)

       The time after which an active SMTPD policy service connection is closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_policy_context (default: empty)

       Optional information that the  Postfix  SMTP  server  specifies  in  the  "policy_context"
       attribute  of  a  policy  service  request (originally, to share the same service endpoint
       among multiple check_policy_service clients).

       This feature is available in Postfix 3.1 and later.

smtpd_policy_service_request_limit (default: 0)

       The maximal number of requests per SMTPD policy service connection, or  zero  (no  limit).
       Once  a  connection reaches this limit, the connection is closed and the next request will
       be sent over a new connection. This is a workaround to avoid  error-recovery  delays  with
       policy servers that cannot maintain a persistent connection.

       This feature is available in Postfix 3.0 and later.

smtpd_policy_service_retry_delay (default: 1s)

       The  delay  between  attempts  to  resend a failed SMTPD policy service request. Specify a
       value greater than zero.

       This feature is available in Postfix 3.0 and later.

smtpd_policy_service_timeout (default: 100s)

       The time limit for connecting to, writing to, or receiving from a delegated  SMTPD  policy
       server.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_try_limit (default: 2)

       The  maximal  number of attempts to send an SMTPD policy service request before giving up.
       Specify a value greater than zero.

       This feature is available in Postfix 3.0 and later.

smtpd_proxy_ehlo (default: $myhostname)

       How the Postfix SMTP server announces itself to the proxy filter.  By default, the Postfix
       hostname is used.

       This feature is available in Postfix 2.1 and later.

smtpd_proxy_filter (default: empty)

       The hostname and TCP port of the mail filtering proxy server.  The proxy receives all mail
       from the Postfix SMTP server, and is supposed to give the result to another  Postfix  SMTP
       server process.

       Specify  "host:port"  or  "inet:host:port"  for  a  TCP endpoint, or "unix:pathname" for a
       UNIX-domain endpoint. The host can be specified as an IP address or as a symbolic name; no
       MX  lookups  are  done.   When  no  "host" or "host:"  are specified, the local machine is
       assumed.  Pathname interpretation is relative to the Postfix queue directory.

       This feature is available in Postfix 2.1 and later.

       The "inet:" and "unix:" prefixes are available in Postfix 2.3 and later.

smtpd_proxy_options (default: empty)

       List of options that control how the Postfix SMTP server communicates with a  before-queue
       content filter. Specify zero or more of the following, separated by comma or whitespace.

       speed_adjust
              Do  not  connect  to a before-queue content filter until an entire message has been
              received. This reduces the  number  of  simultaneous  before-queue  content  filter
              processes.

       NOTE  1:  A  filter  must  not selectively reject recipients of a multi-recipient message.
       Rejecting all recipients is OK, as is accepting all recipients.

       NOTE  2:  This  feature  increases  the  minimum   amount   of   free   queue   space   by
       $message_size_limit. The extra space is needed to save the message to a temporary file.

       This feature is available in Postfix 2.7 and later.

smtpd_proxy_timeout (default: 100s)

       The  time limit for connecting to a proxy filter and for sending or receiving information.
       When a connection fails the client gets  a  generic  error  message  while  more  detailed
       information is logged to the maillog file.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_recipient_limit (default: 1000)

       The maximal number of recipients that the Postfix SMTP server accepts per message delivery
       request.

smtpd_recipient_overshoot_limit (default: 1000)

       The  number  of  recipients  that  a  remote  SMTP  client can send in excess of the limit
       specified with $smtpd_recipient_limit, before  the  Postfix  SMTP  server  increments  the
       per-session error count for each excess recipient.

smtpd_recipient_restrictions (default: see postconf -d output)

       Optional restrictions that the Postfix SMTP server applies in the context of a client RCPT
       TO command, after smtpd_relay_restrictions.   See  SMTPD_ACCESS_README,  section  "Delayed
       evaluation  of  SMTP  access restriction lists" for a discussion of evaluation context and
       time.

       With Postfix versions before 2.10, the rules for relay permission and spam  blocking  were
       combined  under  smtpd_recipient_restrictions, resulting in error-prone configuration.  As
       of   Postfix   2.10,   relay   permission   rules   are   preferably   implemented    with
       smtpd_relay_restrictions,    so   that   a   permissive   spam   blocking   policy   under
       smtpd_recipient_restrictions will no longer result in a permissive mail relay policy.

       For backwards compatibility, sites that migrate from Postfix versions before 2.10 can  set
       smtpd_relay_restrictions  to the empty value, and use smtpd_recipient_restrictions exactly
       as before.

       IMPORTANT:  Either  the  smtpd_relay_restrictions  or   the   smtpd_recipient_restrictions
       parameter  must specify at least one of the following restrictions. Otherwise Postfix will
       refuse to receive mail:

           reject, reject_unauth_destination

           defer, defer_if_permit, defer_unauth_destination

       Specify a list of restrictions, separated by  commas  and/or  whitespace.   Continue  long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The following restrictions are specific to the recipient address that is received with the
       RCPT TO command.

       check_recipient_access type:table
              Search  the  specified access(5) database for the resolved RCPT TO address, domain,
              parent domains, or localpart@, and execute the corresponding action.

       check_recipient_a_access type:table
              Search the specified access(5) database for  the  IP  addresses  for  the  RCPT  TO
              domain,  and  execute  the  corresponding  action.   Note:  a result of "OK" is not
              allowed for safety reasons. Instead, use DUNNO in order to exclude  specific  hosts
              from blacklists.  This feature is available in Postfix 3.0 and later.

       check_recipient_mx_access type:table
              Search  the  specified  access(5) database for the MX hosts for the RCPT TO domain,
              and execute the corresponding action.  Note: a result of "OK" is  not  allowed  for
              safety  reasons.  Instead,  use  DUNNO  in  order  to  exclude  specific hosts from
              blacklists.  This feature is available in Postfix 2.1 and later.

       check_recipient_ns_access type:table
              Search the specified access(5) database for the DNS servers for the RCPT TO domain,
              and  execute  the  corresponding action.  Note: a result of "OK" is not allowed for
              safety reasons. Instead,  use  DUNNO  in  order  to  exclude  specific  hosts  from
              blacklists.  This feature is available in Postfix 2.1 and later.

       permit_auth_destination
              Permit the request when one of the following is true:

       ·      Postfix  is mail forwarder: the resolved RCPT TO domain matches $relay_domains or a
              subdomain  thereof,  and  the  address   contains   no   sender-specified   routing
              (user@elsewhere@domain),

       ·      Postfix   is   the   final   destination:  the  resolved  RCPT  TO  domain  matches
              $mydestination,  $inet_interfaces,  $proxy_interfaces,  $virtual_alias_domains,  or
              $virtual_mailbox_domains,  and  the  address  contains  no sender-specified routing
              (user@elsewhere@domain).

       permit_mx_backup
              Permit the request when the local mail system is backup MX for the RCPT TO  domain,
              or  when  the  domain is an authorized destination (see permit_auth_destination for
              definition).

       ·      Safety: permit_mx_backup does  not  accept  addresses  that  have  sender-specified
              routing information (example: user@elsewhere@domain).

       ·      Safety: permit_mx_backup can be vulnerable to mis-use when access is not restricted
              with permit_mx_backup_networks.

       ·      Safety: as of Postfix version 2.3, permit_mx_backup no longer accepts  the  address
              when  the  local  mail  system  is primary MX for the recipient domain.  Exception:
              permit_mx_backup accepts the address when it specifies  an  authorized  destination
              (see permit_auth_destination for definition).

       ·      Limitation:  mail  may  be  rejected in case of a temporary DNS lookup problem with
              Postfix prior to version 2.0.

       reject_non_fqdn_recipient
              Reject the request when the RCPT TO address specifies  a  domain  that  is  not  in
              fully-qualified domain form, as required by the RFC.
              The  non_fqdn_reject_code  parameter  specifies  the  response  code  for  rejected
              requests (default: 504).

       reject_rhsbl_recipient rbl_domain=d.d.d.d
              Reject the request when the RCPT TO domain is listed with the  A  record  "d.d.d.d"
              under  rbl_domain (Postfix version 2.1 and later only).  Each "d" is a number, or a
              pattern  inside  "[]"  that  contains  one  or  more   ";"-separated   numbers   or
              number..number  ranges  (Postfix  version  2.8  and  later).  If  no  "=d.d.d.d" is
              specified, reject the request when the RCPT TO domain is listed with any  A  record
              under rbl_domain.
              The  maps_rbl_reject_code  parameter  specifies  the  response  code  for  rejected
              requests (default: 554); the  default_rbl_reply  parameter  specifies  the  default
              server reply; and the rbl_reply_maps parameter specifies tables with server replies
              indexed by rbl_domain.  This feature is available in Postfix version 2.0 and later.

       reject_unauth_destination
              Reject the request unless one of the following is true:

       ·      Postfix is mail forwarder: the resolved RCPT TO domain matches $relay_domains or  a
              subdomain     thereof,     and     contains     no     sender-specified     routing
              (user@elsewhere@domain),

       ·      Postfix  is  the  final  destination:  the  resolved   RCPT   TO   domain   matches
              $mydestination,  $inet_interfaces,  $proxy_interfaces,  $virtual_alias_domains,  or
              $virtual_mailbox_domains,    and    contains    no     sender-specified     routing
              (user@elsewhere@domain).
              The  relay_domains_reject_code  parameter  specifies the response code for rejected
              requests (default: 554).

       defer_unauth_destination
              Reject the same requests as reject_unauth_destination, with a  non-permanent  error
              code.  This feature is available in Postfix 2.10 and later.

       reject_unknown_recipient_domain
              Reject  the request when Postfix is not final destination for the recipient domain,
              and the RCPT TO domain has 1) no DNS MX and no DNS A record or 2)  a  malformed  MX
              record  such  as  a  record with a zero-length MX hostname (Postfix version 2.3 and
              later).
              The reply is specified with  the  unknown_address_reject_code  parameter  (default:
              450),  unknown_address_tempfail_action  (default: defer_if_permit), or 556 (nullmx,
              Postfix 3.0 and later). See the respective parameter descriptions for details.

       reject_unlisted_recipient (with Postfix version 2.0: check_recipient_maps)
              Reject the request when the RCPT TO address is not listed  in  the  list  of  valid
              recipients  for its domain class. See the smtpd_reject_unlisted_recipient parameter
              description for details.  This feature is available in Postfix 2.1 and later.

       reject_unverified_recipient
              Reject the request when mail to the RCPT TO address is known to bounce, or when the
              recipient  address  destination is not reachable.  Address verification information
              is managed by the verify(8) server; see the  ADDRESS_VERIFICATION_README  file  for
              details.
              The  unverified_recipient_reject_code  parameter  specifies  the numerical response
              code when an address is known to bounce (default: 450, change into 550 when you are
              confident that it is safe to do so).
              The unverified_recipient_defer_code parameter specifies the numerical response code
              when an address probe failed due to a temporary problem (default: 450).
              The  unverified_recipient_tempfail_action  parameter  specifies  the  action  after
              address probe failure due to a temporary problem (default: defer_if_permit).
              This  feature  breaks  for  aliased addresses with "enable_original_recipient = no"
              (Postfix <= 3.2).
              This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

       ·      Generic restrictions that can be used in any SMTP command context, described  under
              smtpd_client_restrictions.

       ·      SMTP  command  specific  restrictions  described  under  smtpd_client_restrictions,
              smtpd_helo_restrictions and smtpd_sender_restrictions.

       Example:

       # The Postfix before 2.10 default mail relay policy. Later Postfix
       # versions implement this preferably with smtpd_relay_restrictions.
       smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination

smtpd_reject_footer (default: empty)

       Optional information that is appended after each Postfix SMTP server 4XX or 5XX response.

       The following example uses "\c" at the start of the template (supported  in  Postfix  2.10
       and  later)  to  suppress  the line break between the reply text and the footer text. With
       earlier Postfix versions, the footer text always begins on a new line,  and  the  "\c"  is
       output literally.

       /etc/postfix/main.cf:
           smtpd_reject_footer = \c. For assistance, call 800-555-0101.
            Please provide the following information in your problem report:
            time ($localtime), client ($client_address) and server
            ($server_name).

       Server response:

           550-5.5.1 <user@example> Recipient address rejected: User
           unknown. For assistance, call 800-555-0101. Please provide the
           following information in your problem report: time (Jan 4 15:42:00),
           client (192.168.1.248) and server (mail1.example.com).

       Note:  the above text is meant to make it easier to find the Postfix logfile records for a
       failed SMTP session. The text itself is not logged to the Postfix  SMTP  server's  maillog
       file.

       Be  sure  to  keep  the text as short as possible. Long text may be truncated before it is
       logged to the remote SMTP client's maillog file, or before it is returned to the sender in
       a delivery status notification.

       This  feature  supports a limited number of $name attributes in the footer text. These are
       replaced by their current value for the SMTP session:

       client_address
              The Client IP address that is logged in the maillog file.

       client_port
              The client TCP port that is logged in the maillog file.

       localtime
              The server local time (Mmm dd hh:mm:ss) that is logged in the maillog file.

       server_name
              The server's myhostname value.  This attribute is made  available  for  sites  with
              multiple  MTAs (perhaps behind a load-balancer), where the server name can help the
              server support team to quickly find the right log files.

       Notes:

       ·      NOT  SUPPORTED  are  other  attributes  such  as  sender,  recipient,  or   main.cf
              parameters.

       ·      For safety reasons, text that does not match $smtpd_expansion_filter is censored.

       This  feature  supports the two-character sequence \n as a request for a line break in the
       footer text. Postfix automatically inserts after each  line  break  the  three-digit  SMTP
       reply code (and optional enhanced status code) from the original Postfix reject message.

       To   work   around   mail  software  that  mis-handles  multi-line  replies,  specify  the
       two-character sequence \c at the start of the template.  This suppresses  the  line  break
       between the reply text and the footer text (Postfix 2.10 and later).

       This feature is available in Postfix 2.8 and later.

smtpd_reject_unlisted_recipient (default: yes)

       Request  that  the  Postfix SMTP server rejects mail for unknown recipient addresses, even
       when no explicit reject_unlisted_recipient access restriction is specified. This  prevents
       the Postfix queue from filling up with undeliverable MAILER-DAEMON messages.

       An  address  is  always  considered  "known"  when  it  matches  a  virtual(5)  alias or a
       canonical(5) mapping.

       ·      The recipient domain matches $mydestination, $inet_interfaces or $proxy_interfaces,
              but the recipient is not listed in $local_recipient_maps, and $local_recipient_maps
              is not null.

       ·      The recipient domain matches $virtual_alias_domains but the recipient is not listed
              in $virtual_alias_maps.

       ·      The  recipient  domain  matches  $virtual_mailbox_domains  but the recipient is not
              listed in $virtual_mailbox_maps, and $virtual_mailbox_maps is not null.

       ·      The recipient domain matches $relay_domains but the  recipient  is  not  listed  in
              $relay_recipient_maps, and $relay_recipient_maps is not null.

       This feature is available in Postfix 2.1 and later.

smtpd_reject_unlisted_sender (default: no)

       Request that the Postfix SMTP server rejects mail from unknown sender addresses, even when
       no explicit reject_unlisted_sender access restriction is specified. This can slow down  an
       explosion of forged mail from worms or viruses.

       An  address  is  always  considered  "known"  when  it  matches  a  virtual(5)  alias or a
       canonical(5) mapping.

       ·      The sender domain matches $mydestination,  $inet_interfaces  or  $proxy_interfaces,
              but the sender is not listed in $local_recipient_maps, and $local_recipient_maps is
              not null.

       ·      The sender domain matches $virtual_alias_domains but the sender is  not  listed  in
              $virtual_alias_maps.

       ·      The  sender domain matches $virtual_mailbox_domains but the sender is not listed in
              $virtual_mailbox_maps, and $virtual_mailbox_maps is not null.

       ·      The  sender  domain  matches  $relay_domains  but  the  sender  is  not  listed  in
              $relay_recipient_maps, and $relay_recipient_maps is not null.

       This feature is available in Postfix 2.1 and later.

smtpd_relay_restrictions (default: permit_mynetworks, permit_sasl_authenticated,

       defer_unauth_destination)
       Access restrictions for mail relay control that the Postfix SMTP  server  applies  in  the
       context    of   the   RCPT   TO   command,   before   smtpd_recipient_restrictions.    See
       SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access restriction lists"  for  a
       discussion of evaluation context and time.

       With  Postfix  versions before 2.10, the rules for relay permission and spam blocking were
       combined under smtpd_recipient_restrictions, resulting in error-prone  configuration.   As
       of    Postfix   2.10,   relay   permission   rules   are   preferably   implemented   with
       smtpd_relay_restrictions,   so   that   a   permissive   spam   blocking   policy    under
       smtpd_recipient_restrictions will no longer result in a permissive mail relay policy.

       For  backwards compatibility, sites that migrate from Postfix versions before 2.10 can set
       smtpd_relay_restrictions to the empty value, and use smtpd_recipient_restrictions  exactly
       as before.

       By default, the Postfix SMTP server accepts:

       ·      Mail from clients whose IP address matches $mynetworks, or:

       ·      Mail  to  remote  destinations that match $relay_domains, except for addresses that
              contain sender-specified routing (user@elsewhere@domain), or:

       ·      Mail to  local  destinations  that  match  $inet_interfaces  or  $proxy_interfaces,
              $mydestination, $virtual_alias_domains, or $virtual_mailbox_domains.

       IMPORTANT:   Either   the  smtpd_relay_restrictions  or  the  smtpd_recipient_restrictions
       parameter must specify at least one of the following restrictions. Otherwise Postfix  will
       refuse to receive mail:

           reject, reject_unauth_destination

           defer, defer_if_permit, defer_unauth_destination

       Specify  a  list  of  restrictions,  separated by commas and/or whitespace.  Continue long
       lines by starting the next line with whitespace.  The same restrictions are  available  as
       documented under smtpd_recipient_restrictions.

       This feature is available in Postix 2.10 and later.

smtpd_restriction_classes (default: empty)

       User-defined  aliases  for  groups of access restrictions. The aliases can be specified in
       smtpd_recipient_restrictions etc., and on the  right-hand  side  of  a  Postfix  access(5)
       table.

       One   major   application   is  for  implementing  per-recipient  UCE  control.   See  the
       RESTRICTION_CLASS_README document for other examples.

smtpd_sasl_application_name (default: smtpd)

       The application name that the Postfix SMTP server uses  for  SASL  server  initialization.
       This  controls  the  name  of  the  SASL  configuration  file. The default value is smtpd,
       corresponding to a SASL configuration file named smtpd.conf.

       This feature is available in Postfix 2.1 and 2.2. With  Postfix  2.3  it  was  renamed  to
       smtpd_sasl_path.

smtpd_sasl_auth_enable (default: no)

       Enable SASL authentication in the Postfix SMTP server. By default, the Postfix SMTP server
       does not use authentication.

       If a remote SMTP client is authenticated, the permit_sasl_authenticated access restriction
       can be used to permit relay access, like this:

           # With Postfix 2.10 and later, the mail relay policy is
           # preferably specified under smtpd_relay_restrictions.
           smtpd_relay_restrictions =
               permit_mynetworks, permit_sasl_authenticated, ...

       # With Postfix before 2.10, the relay policy can be
       # specified only under smtpd_recipient_restrictions.
       smtpd_recipient_restrictions =
           permit_mynetworks, permit_sasl_authenticated, ...

       To reject all SMTP connections from unauthenticated clients, specify "smtpd_delay_reject =
       yes" (which is the default) and use:

           smtpd_client_restrictions = permit_sasl_authenticated, reject

       See the SASL_README file for SASL configuration and operation details.

smtpd_sasl_authenticated_header (default: no)

       Report the SASL authenticated user name in the smtpd(8) Received message header.

       This feature is available in Postfix 2.3 and later.

smtpd_sasl_exceptions_networks (default: empty)

       What remote SMTP clients the Postfix SMTP server will not offer AUTH support to.

       Some clients (Netscape 4 at least) have a bug that causes them  to  require  a  login  and
       password  whenever  AUTH  is  offered, whether it's necessary or not. To work around this,
       specify, for example, $mynetworks to prevent Postfix from offering AUTH to local clients.

       Specify a list of network/netmask patterns, separated by  commas  and/or  whitespace.  The
       mask  specifies  the  number  of  bits in the network part of a host address. You can also
       "/file/name" or  "type:table"  patterns.   A  "/file/name"  pattern  is  replaced  by  its
       contents;  a  "type:table"  lookup  table  is  matched when a table entry matches a lookup
       string (the lookup result is ignored).  Continue long lines by starting the next line with
       whitespace.  Specify "!pattern" to exclude an address or network block from the list.  The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note:  IP  version  6  address  information  must  be   specified   inside   []   in   the
       smtpd_sasl_exceptions_networks  value,  and  in  files  specified  with  "/file/name".  IP
       version 6 addresses contain the ":" character, and would  otherwise  be  confused  with  a
       "type:table" pattern.

       Example:

       smtpd_sasl_exceptions_networks = $mynetworks

       This feature is available in Postfix 2.1 and later.

smtpd_sasl_local_domain (default: empty)

       The name of the Postfix SMTP server's local SASL authentication realm.

       By default, the local authentication realm name is the null string.

       Examples:

       smtpd_sasl_local_domain = $mydomain
       smtpd_sasl_local_domain = $myhostname

smtpd_sasl_path (default: smtpd)

       Implementation-specific  information  that  the  Postfix SMTP server passes through to the
       SASL plug-in  implementation  that  is  selected  with  smtpd_sasl_type.   Typically  this
       specifies the name of a configuration file or rendezvous point.

       This  feature  is  available  in  Postfix 2.3 and later. In earlier releases it was called
       smtpd_sasl_application_name.

smtpd_sasl_security_options (default: noanonymous)

       Postfix SMTP server SASL security options;  as  of  Postfix  2.3  the  list  of  available
       features depends on the SASL server implementation that is selected with smtpd_sasl_type.

       The following security features are defined for the cyrus server SASL implementation:

       Restrict  what authentication mechanisms the Postfix SMTP server will offer to the client.
       The list of available authentication mechanisms is system dependent.

       Specify zero or more of the following:

       noplaintext
              Disallow methods that use plaintext passwords.

       noactive
              Disallow methods subject to active (non-dictionary) attack.

       nodictionary
              Disallow methods subject to passive (dictionary) attack.

       noanonymous
              Disallow methods that allow anonymous authentication.

       forward_secrecy
              Only allow methods that support forward secrecy (Dovecot only).

       mutual_auth
              Only allow methods that provide mutual authentication  (not  available  with  Cyrus
              SASL version 1).

       By default, the Postfix SMTP server accepts plaintext passwords but not anonymous logins.

       Warning:  it appears that clients try authentication methods in the order as advertised by
       the server (e.g., PLAIN ANONYMOUS CRAM-MD5) which means  that  if  you  disable  plaintext
       passwords, clients will log in anonymously, even when they should be able to use CRAM-MD5.
       So, if you disable  plaintext  logins,  disable  anonymous  logins  too.   Postfix  treats
       anonymous login as no authentication.

       Example:

       smtpd_sasl_security_options = noanonymous, noplaintext

smtpd_sasl_service (default: smtp)

       The  service name that is passed to the SASL plug-in that is selected with smtpd_sasl_type
       and smtpd_sasl_path.

       This feature is available in Postfix 2.11 and later. Prior versions behave as if "smtp" is
       specified.

smtpd_sasl_tls_security_options (default: $smtpd_sasl_security_options)

       The  SASL  authentication  security  options  that  the  Postfix  SMTP server uses for TLS
       encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtpd_sasl_type (default: cyrus)

       The SASL plug-in type that the Postfix SMTP server  should  use  for  authentication.  The
       available types are listed with the "postconf -a" command.

       This feature is available in Postfix 2.3 and later.

smtpd_sender_login_maps (default: empty)

       Optional lookup table with the SASL login names that own the sender (MAIL FROM) addresses.

       Specify  zero  or more "type:name" lookup tables, separated by whitespace or comma. Tables
       will be searched in the specified order until a match is found.  With lookups from indexed
       files  such as DB or DBM, or from networked tables such as NIS, LDAP or SQL, the following
       search operations are done with a sender address of user@domain:

       1) user@domain
              This table lookup is always done and has the highest precedence.

       2) user
              This table lookup is done only when the domain part of the sender  address  matches
              $myorigin, $mydestination, $inet_interfaces or $proxy_interfaces.

       3) @domain
              This table lookup is done last and has the lowest precedence.

       In all cases the result of table lookup must be either "not found" or a list of SASL login
       names separated by comma and/or whitespace.

smtpd_sender_restrictions (default: empty)

       Optional restrictions that the Postfix SMTP server applies in the context of a client MAIL
       FROM  command.   See  SMTPD_ACCESS_README,  section  "Delayed  evaluation  of  SMTP access
       restriction lists" for a discussion of evaluation context and time.

       The default is to permit everything.

       Specify a list of restrictions, separated by  commas  and/or  whitespace.   Continue  long
       lines by starting the next line with whitespace.  Restrictions are applied in the order as
       specified; the first restriction that matches wins.

       The following restrictions are specific to the sender address received with the MAIL  FROM
       command.

       check_sender_access type:table
              Search  the  specified access(5) database for the MAIL FROM address, domain, parent
              domains, or localpart@, and execute the corresponding action.

       check_sender_a_access type:table
              Search the specified access(5) database for the IP  addresses  for  the  MAIL  FROM
              domain,  and  execute  the  corresponding  action.   Note:  a result of "OK" is not
              allowed for safety reasons. Instead, use DUNNO in order to exclude  specific  hosts
              from blacklists.  This feature is available in Postfix 3.0 and later.

       check_sender_mx_access type:table
              Search  the specified access(5) database for the MX hosts for the MAIL FROM domain,
              and execute the corresponding action.  Note: a result of "OK" is  not  allowed  for
              safety  reasons.  Instead,  use  DUNNO  in  order  to  exclude  specific hosts from
              blacklists.  This feature is available in Postfix 2.1 and later.

       check_sender_ns_access type:table
              Search the specified access(5) database for the  DNS  servers  for  the  MAIL  FROM
              domain,  and  execute  the  corresponding  action.   Note:  a result of "OK" is not
              allowed for safety reasons. Instead, use DUNNO in order to exclude  specific  hosts
              from blacklists.  This feature is available in Postfix 2.1 and later.

       reject_authenticated_sender_login_mismatch
              Enforces  the  reject_sender_login_mismatch  restriction  for authenticated clients
              only. This feature is available in Postfix version 2.1 and later.

       reject_known_sender_login_mismatch
              Apply the reject_sender_login_mismatch restriction only to MAIL FROM addresses that
              are  known  in  $smtpd_sender_login_maps.   This  feature  is  available in Postfix
              version 2.11 and later.

       reject_non_fqdn_sender
              Reject the request when the MAIL FROM address specifies a domain  that  is  not  in
              fully-qualified domain form as required by the RFC.
              The  non_fqdn_reject_code  parameter  specifies  the  response  code  for  rejected
              requests (default: 504).

       reject_rhsbl_sender rbl_domain=d.d.d.d
              Reject the request when the MAIL FROM domain is listed with the A record  "d.d.d.d"
              under  rbl_domain (Postfix version 2.1 and later only).  Each "d" is a number, or a
              pattern  inside  "[]"  that  contains  one  or  more   ";"-separated   numbers   or
              number..number  ranges  (Postfix  version  2.8  and  later).  If  no  "=d.d.d.d" is
              specified, reject the request when the MAIL FROM domain is listed with any A record
              under rbl_domain.
              The  maps_rbl_reject_code  parameter  specifies  the  response  code  for  rejected
              requests (default:  554); the default_rbl_reply  parameter  specifies  the  default
              server reply; and the rbl_reply_maps parameter specifies tables with server replies
              indexed by rbl_domain.  This feature is available in Postfix 2.0 and later.

       reject_sender_login_mismatch
              Reject the request when $smtpd_sender_login_maps specifies an owner  for  the  MAIL
              FROM  address,  but  the  client  is not (SASL) logged in as that MAIL FROM address
              owner; or when the client is (SASL) logged in, but the client  login  name  doesn't
              own the MAIL FROM address according to $smtpd_sender_login_maps.

       reject_unauthenticated_sender_login_mismatch
              Enforces  the  reject_sender_login_mismatch restriction for unauthenticated clients
              only. This feature is available in Postfix version 2.1 and later.

       reject_unknown_sender_domain
              Reject the request when Postfix is not final destination for  the  sender  address,
              and the MAIL FROM domain has 1) no DNS MX and no DNS A record, or 2) a malformed MX
              record such as a record with a zero-length MX hostname  (Postfix  version  2.3  and
              later).
              The  reply  is  specified  with the unknown_address_reject_code parameter (default:
              450), unknown_address_tempfail_action (default: defer_if_permit), or  550  (nullmx,
              Postfix 3.0 and later). See the respective parameter descriptions for details.

       reject_unlisted_sender
              Reject  the  request  when the MAIL FROM address is not listed in the list of valid
              recipients for its domain class.  See  the  smtpd_reject_unlisted_sender  parameter
              description for details.  This feature is available in Postfix 2.1 and later.

       reject_unverified_sender
              Reject  the  request when mail to the MAIL FROM address is known to bounce, or when
              the sender address destination is not reachable.  Address verification  information
              is  managed  by  the verify(8) server; see the ADDRESS_VERIFICATION_README file for
              details.
              The unverified_sender_reject_code parameter specifies the numerical  response  code
              when  an  address  is  known  to bounce (default: 450, change into 550 when you are
              confident that it is safe to do so).
              The unverified_sender_defer_code specifies the  numerical  response  code  when  an
              address probe failed due to a temporary problem (default: 450).
              The  unverified_sender_tempfail_action parameter specifies the action after address
              probe failure due to a temporary problem (default: defer_if_permit).
              This feature breaks for aliased addresses  with  "enable_original_recipient  =  no"
              (Postfix <= 3.2).
              This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

       ·      Generic  restrictions that can be used in any SMTP command context, described under
              smtpd_client_restrictions.

       ·      SMTP command specific restrictions described  under  smtpd_client_restrictions  and
              smtpd_helo_restrictions.

       ·      SMTP  command  specific  restrictions described under smtpd_recipient_restrictions.
              When recipient restrictions are listed under smtpd_sender_restrictions,  they  have
              effect  only with "smtpd_delay_reject = yes", so that $smtpd_sender_restrictions is
              evaluated at the time of the RCPT TO command.

       Examples:

       smtpd_sender_restrictions = reject_unknown_sender_domain
       smtpd_sender_restrictions = reject_unknown_sender_domain,
           check_sender_access hash:/etc/postfix/access

smtpd_service_name (default: smtpd)

       The internal service that postscreen(8) hands off allowed  connections  to.  In  a  future
       version there may be different classes of SMTP service.

       This feature is available in Postfix 2.8.

smtpd_soft_error_limit (default: 10)

       The  number  of  errors  a  remote  SMTP client is allowed to make without delivering mail
       before the Postfix SMTP server slows down all its responses.

       ·      With Postfix version 2.1 and later, the Postfix SMTP server delays all responses by
              $smtpd_error_sleep_time seconds.

       ·      With Postfix versions 2.0 and earlier, the Postfix SMTP server delays all responses
              by (number of errors) seconds.

smtpd_starttls_timeout (default: see postconf -d output)

       The time limit for Postfix SMTP server write and read operations during  TLS  startup  and
       shutdown  handshake  procedures.  The  current  default  value is stress-dependent. Before
       Postfix version 2.8, it was fixed at 300s.

       This feature is available in Postfix 2.2 and later.

smtpd_timeout (default: normal: 300s, overload: 10s)

       The time limit for sending a Postfix SMTP server response and for receiving a remote  SMTP
       client  request. Normally the default limit is 300s, but it changes under overload to just
       10s. With Postfix 2.5 and earlier, the SMTP server always uses a time  limit  of  300s  by
       default.

       Note:  if  you set SMTP time limits to very large values you may have to update the global
       ipc_timeout parameter.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

smtpd_tls_CAfile (default: empty)

       A  file  containing (PEM format) CA certificates of root CAs trusted to sign either remote
       SMTP client certificates or intermediate CA certificates.  These are  loaded  into  memory
       before  the  smtpd(8)  server  enters  the  chroot jail. If the number of trusted roots is
       large, consider using smtpd_tls_CApath instead, but note that the latter directory must be
       present  in the chroot jail if the smtpd(8) server is chrooted. This file may also be used
       to augment the server certificate trust chain, but it is best to include all the  required
       certificates directly in the server certificate file.

       Specify  "smtpd_tls_CAfile  =  /path/to/system_CA_file"  to  use  ONLY the system-supplied
       default Certification Authority certificates.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending the system-supplied
       default CAs and trusting third-party certificates.

       By   default  (see  smtpd_tls_ask_ccert),  client  certificates  are  not  requested,  and
       smtpd_tls_CAfile should remain empty. If you do  make  use  of  client  certificates,  the
       distinguished  names (DNs) of the Certification Authorities listed in smtpd_tls_CAfile are
       sent to the remote SMTP client in  the  client  certificate  request  message.  MUAs  with
       multiple  client  certificates  may use the list of preferred Certification Authorities to
       select the correct client certificate.  You may want to put your "preferred" CA or CAs  in
       this file, and install other trusted CAs in $smtpd_tls_CApath.

       Example:

       smtpd_tls_CAfile = /etc/postfix/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_CApath (default: empty)

       A  directory  containing  (PEM  format) CA certificates of root CAs trusted to sign either
       remote SMTP client certificates or intermediate CA certificates. Do not forget  to  create
       the    necessary    "hash"    links   with,   for   example,   "$OPENSSL_HOME/bin/c_rehash
       /etc/postfix/certs". To use smtpd_tls_CApath in chroot mode, this directory  (or  a  copy)
       must be inside the chroot jail.

       Specify  "smtpd_tls_CApath = /path/to/system_CA_directory" to use ONLY the system-supplied
       default Certification Authority certificates.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending the system-supplied
       default CAs and trusting third-party certificates.

       By   default  (see  smtpd_tls_ask_ccert),  client  certificates  are  not  requested,  and
       smtpd_tls_CApath  should  remain  empty.  In  contrast   to   smtpd_tls_CAfile,   DNs   of
       Certification  Authorities  installed  in $smtpd_tls_CApath are not included in the client
       certificate request message. MUAs with multiple client certificates may use  the  list  of
       preferred  Certification  Authorities  to  select the correct client certificate.  You may
       want to put your "preferred" CA or CAs in $smtpd_tls_CAfile,  and  install  the  remaining
       trusted CAs in $smtpd_tls_CApath.

       Example:

       smtpd_tls_CApath = /etc/postfix/certs

       This feature is available in Postfix 2.2 and later.

smtpd_tls_always_issue_session_ids (default: yes)

       Force  the Postfix SMTP server to issue a TLS session id, even when TLS session caching is
       turned off (smtpd_tls_session_cache_database is empty). This behavior is  compatible  with
       Postfix < 2.3.

       With  Postfix 2.3 and later the Postfix SMTP server can disable session id generation when
       TLS session caching is turned off. This keeps remote SMTP clients  from  caching  sessions
       that almost certainly cannot be re-used.

       By  default, the Postfix SMTP server always generates TLS session ids. This works around a
       known defect in mail client  applications  such  as  MS  Outlook,  and  may  also  prevent
       interoperability issues with other MTAs.

       Example:

       smtpd_tls_always_issue_session_ids = no

       This feature is available in Postfix 2.3 and later.

smtpd_tls_ask_ccert (default: no)

       Ask  a  remote  SMTP  client  for  a  client  certificate.  This information is needed for
       certificate based mail relaying with, for example, the permit_tls_clientcerts feature.

       Some clients such as Netscape will either complain if no certificate is available (for the
       list  of  CAs  in  $smtpd_tls_CAfile) or will offer multiple client certificates to choose
       from. This may be annoying, so this option is "off" by default.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_auth_only (default: no)

       When TLS encryption is optional in the Postfix SMTP server, do not announce or accept SASL
       authentication over unencrypted connections.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_ccert_verifydepth (default: 9)

       The  verification depth for remote SMTP client certificates. A depth of 1 is sufficient if
       the issuing CA is listed in a local CA file.

       The default verification depth is 9 (the OpenSSL default) for compatibility  with  earlier
       Postfix  behavior.  Prior  to  Postfix 2.5, the default value was 5, but the limit was not
       actually enforced. If you have set this to a lower non-default  value,  certificates  with
       longer trust chains may now fail to verify. Certificate chains with 1 or 2 CAs are common,
       deeper chains are more rare and any number between 5 and 9 should suffice in practice. You
       can  choose  a  lower number if, for example, you trust certificates directly signed by an
       issuing CA but not any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_cert_file (default: empty)

       File with the Postfix SMTP server RSA certificate in  PEM  format.   This  file  may  also
       contain the Postfix SMTP server private RSA key.

       Public  Internet  MX  hosts without certificates signed by a "reputable" CA must generate,
       and  be  prepared  to  present  to  most  clients,  a  self-signed  or  private-CA  signed
       certificate.  The  client  will  not  be able to authenticate the server, but unless it is
       running Postfix 2.3 or similar software, it will still insist on a server certificate.

       For servers that are not public Internet MX hosts,  Postfix  2.3  supports  configurations
       with  no  certificates.  This entails the use of just the anonymous TLS ciphers, which are
       not supported by typical SMTP clients. Since such clients will not, as a rule,  fall  back
       to  plain  text  after a TLS handshake failure, the server will be unable to receive email
       from TLS enabled clients. To avoid accidental configurations with no certificates, Postfix
       2.3  enables  certificate-less  operation  only  when  the  administrator  explicitly sets
       "smtpd_tls_cert_file = none". This  ensures  that  new  Postfix  configurations  will  not
       accidentally run with no certificates.

       Both RSA and DSA certificates are supported.  When both types are present, the cipher used
       determines which certificate will be presented to the client.  For  Netscape  and  OpenSSL
       clients without special cipher choices the RSA certificate is preferred.

       To  enable a remote SMTP client to verify the Postfix SMTP server certificate, the issuing
       CA certificates must be made available to the client.  You  should  include  the  required
       certificates  in  the  server  certificate  file,  the  server certificate first, then the
       issuing CA(s) (bottom-up order).

       Example: the certificate for "server.example.com" was issued by  "intermediate  CA"  which
       itself   has   a  certificate  of  "root  CA".   Create  the  server.pem  file  with  "cat
       server_cert.pem intermediate_CA.pem root_CA.pem > server.pem".

       If you also want to verify client certificates issued by these CAs, you  can  add  the  CA
       certificates  to  the  smtpd_tls_CAfile, in which case it is not necessary to have them in
       the smtpd_tls_cert_file or smtpd_tls_dcert_file.

       A certificate supplied here must be usable as an SSL server certificate and hence pass the
       "openssl verify -purpose sslserver ..." test.

       Example:

       smtpd_tls_cert_file = /etc/postfix/server.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_cipherlist (default: empty)

       Obsolete  Postfix < 2.3 control for the Postfix SMTP server TLS cipher list. It is easy to
       create interoperability problems by choosing a non-default  cipher  list.  Do  not  use  a
       non-default TLS cipherlist for MX hosts on the public Internet. Clients that begin the TLS
       handshake, but are unable to agree on a common cipher, may not be able to send  any  email
       to the SMTP server. Using a restricted cipher list may be more appropriate for a dedicated
       MSA or an internal mailhub, where one can exert some control over  the  TLS  software  and
       settings of the connecting clients.

       Note: do not use "" quotes around the parameter value.

       This  feature  is  available with Postfix version 2.2. It is not used with Postfix 2.3 and
       later; use smtpd_tls_mandatory_ciphers instead.

smtpd_tls_ciphers (default: medium)

       The minimum TLS cipher grade that the Postfix SMTP server will use with opportunistic  TLS
       encryption.  Cipher  types  listed in smtpd_tls_exclude_ciphers are excluded from the base
       definition of the selected cipher grade.   The  default  value  is  "medium"  for  Postfix
       releases after the middle of 2015, "export" for older releases.

       When  TLS  is  mandatory  the  cipher  grade is chosen via the smtpd_tls_mandatory_ciphers
       configuration parameter, see there for syntax details.

       This feature is available in Postfix 2.6 and later. With earlier Postfix releases only the
       smtpd_tls_mandatory_ciphers  parameter  is  implemented, and opportunistic TLS always uses
       "export" or better (i.e. all) ciphers.

smtpd_tls_dcert_file (default: empty)

       File with the Postfix SMTP server DSA certificate in  PEM  format.   This  file  may  also
       contain the Postfix SMTP server private DSA key.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_dcert_file = /etc/postfix/server-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_dh1024_param_file (default: empty)

       File  with  DH  parameters  that  the  Postfix  SMTP server should use with non-export EDH
       ciphers.

       Instead of using the exact same parameter sets as distributed with other TLS packages,  it
       is  more  secure  to generate your own set of parameters with something like the following
       commands:

           openssl dhparam -out /etc/postfix/dh512.pem 512
           openssl dhparam -out /etc/postfix/dh1024.pem 1024
           openssl dhparam -out /etc/postfix/dh2048.pem 2048

       It is safe to share the same DH parameters between multiple  Postfix  instances.   If  you
       prefer, you can generate separate parameters for each instance.

       If  you  want  to  take  maximal  advantage  of ciphers that offer forward secrecy see the
       Getting  started  section  of  FORWARD_SECRECY_README.   The  full  document  conveniently
       presents  all  information  about  Postfix "perfect" forward secrecy support in one place:
       what forward secrecy is, how to tweak settings, and  what  you  can  expect  to  see  when
       Postfix uses ciphers with forward secrecy.

       Example:

       smtpd_tls_dh1024_param_file = /etc/postfix/dh2048.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dh512_param_file (default: empty)

       File  with  DH  parameters  that  the Postfix SMTP server should use with export-grade EDH
       ciphers.  The default SMTP server cipher grade is "medium" with Postfix releases after the
       middle of 2015, and as a result export-grade cipher suites are by default not used.

       See also the discussion under the smtpd_tls_dh1024_param_file configuration parameter.

       Example:

       smtpd_tls_dh512_param_file = /etc/postfix/dh_512.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dkey_file (default: $smtpd_tls_dcert_file)

       File  with  the  Postfix  SMTP  server  DSA  private  key in PEM format.  This file may be
       combined  with  the  Postfix   SMTP   server   DSA   certificate   file   specified   with
       $smtpd_tls_dcert_file.

       The  private  key must be accessible without a pass-phrase, i.e. it must not be encrypted.
       File permissions should grant read-only access to the system superuser  account  ("root"),
       and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_eccert_file (default: empty)

       File  with  the  Postfix  SMTP server ECDSA certificate in PEM format.  This file may also
       contain the Postfix SMTP server private ECDSA key.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_eccert_file = /etc/postfix/ecdsa-scert.pem

       This feature is available in Postfix 2.6 and later, when Postfix is  compiled  and  linked
       with OpenSSL 1.0.0 or later.

smtpd_tls_eckey_file (default: $smtpd_tls_eccert_file)

       File  with  the  Postfix  SMTP  server  ECDSA private key in PEM format.  This file may be
       combined  with  the  Postfix  SMTP  server   ECDSA   certificate   file   specified   with
       $smtpd_tls_eccert_file.

       The  private  key must be accessible without a pass-phrase, i.e. it must not be encrypted.
       File permissions should grant read-only access to the system superuser  account  ("root"),
       and no access to anyone else.

       This  feature  is  available in Postfix 2.6 and later, when Postfix is compiled and linked
       with OpenSSL 1.0.0 or later.

smtpd_tls_eecdh_grade (default: see postconf -d output)

       The Postfix SMTP server security grade for ephemeral elliptic-curve Diffie-Hellman (EECDH)
       key exchange.

       The available choices are:

       none   Don't  use EECDH. Ciphers based on EECDH key exchange will be disabled. This is the
              default in Postfix versions 2.6 and 2.7.

       strong Use EECDH with approximately 128 bits of security  at  a  reasonable  computational
              cost.   This   is   the   current  best-practice  trade-off  between  security  and
              computational efficiency. This is the default in Postfix version 2.8 and later.

       ultra  Use EECDH with approximately 192 bits of security at  computational  cost  that  is
              approximately  twice  as high as 128 bit strength ECC. Barring significant progress
              in attacks on elliptic curve crypto-systems, the "strong" curve is  sufficient  for
              most users.

       auto   Use  the  most preferred curve that is supported by both the client and the server.
              This setting requires Postfix >= 3.2 compiled and linked  with  OpenSSL  >=  1.0.2.
              This is the default setting under the above conditions.

       If  you  want  to  take  maximal  advantage  of ciphers that offer forward secrecy see the
       Getting  started  section  of  FORWARD_SECRECY_README.   The  full  document  conveniently
       presents  all  information  about  Postfix "perfect" forward secrecy support in one place:
       what forward secrecy is, how to tweak settings, and  what  you  can  expect  to  see  when
       Postfix uses ciphers with forward secrecy.

       This  feature  is  available in Postfix 2.6 and later, when it is compiled and linked with
       OpenSSL 1.0.0 or later on platforms where EC algorithms have  not  been  disabled  by  the
       vendor.

smtpd_tls_exclude_ciphers (default: empty)

       List  of  ciphers  or  cipher types to exclude from the SMTP server cipher list at all TLS
       security levels. Excluding valid ciphers can  create  interoperability  problems.  DO  NOT
       exclude  ciphers unless it is essential to do so. This is not an OpenSSL cipherlist; it is
       a simple list separated by whitespace and/or commas. The elements are a single cipher,  or
       one  or  more "+" separated cipher properties, in which case only ciphers matching all the
       properties are excluded.

       Examples (some of these will cause problems):

           smtpd_tls_exclude_ciphers = aNULL
           smtpd_tls_exclude_ciphers = MD5, DES
           smtpd_tls_exclude_ciphers = DES+MD5
           smtpd_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
           smtpd_tls_exclude_ciphers = kEDH+aRSA

       The first setting disables anonymous ciphers. The next setting disables ciphers  that  use
       the  MD5  digest  algorithm  or  the  (single)  DES encryption algorithm. The next setting
       disables ciphers that use MD5 and DES together.  The next setting disables the two ciphers
       "AES256-SHA"  and  "DES-CBC3-MD5".  The  last  setting disables ciphers that use "EDH" key
       exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtpd_tls_fingerprint_digest (default: md5)

       The message digest algorithm to construct remote SMTP client-certificate  fingerprints  or
       public   key   fingerprints   (Postfix   2.9   and   later)   for  check_ccert_access  and
       permit_tls_clientcerts. The default algorithm is md5,  for  backwards  compatibility  with
       Postfix releases prior to 2.5.

       Advances in hash function cryptanalysis have led to md5 being deprecated in favor of sha1.
       However, as long as there are no known "second pre-image" attacks against md5, its use  in
       this context can still be considered safe.

       While  additional  digest  algorithms  are  often available with OpenSSL's libcrypto, only
       those used by libssl in SSL cipher suites are available to Postfix.

       To find the fingerprint of a specific certificate file, with a specific digest  algorithm,
       run:

           $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The text to the right of "=" sign is the desired fingerprint.  For example:

           $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
           SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       To  extract  the public key fingerprint from an X.509 certificate, you need to extract the
       public key from the certificate and compute the appropriate  digest  of  its  DER  (ASN.1)
       encoding.  With OpenSSL the "-pubkey" option of the "x509" command extracts the public key
       always in "PEM" format. We pipe the result to another OpenSSL command  that  converts  the
       key to DER and then to the "dgst" command to compute the fingerprint.

       The  actual  command  to transform the key to DER format depends on the version of OpenSSL
       used. With OpenSSL 1.0.0 and later, the  "pkey"  command  supports  all  key  types.  With
       OpenSSL  0.9.8  and  earlier, the key type is always RSA (nobody uses DSA, and EC keys are
       not fully supported by 0.9.8), so the "rsa" command is used.

           # OpenSSL 1.0 with all certificates and SHA-1 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl pkey -pubin -outform DER |
               openssl dgst -sha1 -c
           (stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:8b:fc:09:1a:61:98:b5:bc:7c:60:58

           # OpenSSL 0.9.8 with RSA certificates and MD5 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl rsa -pubin -outform DER |
               openssl dgst -md5 -c
           (stdin)= f4:62:60:f6:12:8f:d5:8d:28:4d:13:a7:db:b2:ff:50

       The Postfix SMTP server and client log the peer (leaf) certificate fingerprint and  public
       key fingerprint when the TLS loglevel is 2 or higher.

       Note:  Postfix  2.9.0-2.9.5  computed  the  public  key  fingerprint  incorrectly.  To use
       public-key fingerprints, upgrade to Postfix 2.9.6 or later.

       Example: client-certificate access table, with sha1 fingerprints:

           /etc/postfix/main.cf:
               smtpd_tls_fingerprint_digest = sha1
               smtpd_client_restrictions =
                   check_ccert_access hash:/etc/postfix/access,
                   reject
           /etc/postfix/access:
               # Action folded to next line...
               AF:88:7C:AD:51:95:6F:36:96:F6:01:FB:2E:48:CD:AB:49:25:A2:3B
                   OK
               85:16:78:FD:73:6E:CE:70:E0:31:5F:0D:3C:C8:6D:C4:2C:24:59:E1
                   permit_auth_destination

       This feature is available in Postfix 2.5 and later.

smtpd_tls_key_file (default: $smtpd_tls_cert_file)

       File with the Postfix SMTP server RSA private  key  in  PEM  format.   This  file  may  be
       combined   with   the   Postfix   SMTP   server   RSA   certificate  file  specified  with
       $smtpd_tls_cert_file.

       The private key must be accessible without a pass-phrase, i.e. it must not  be  encrypted.
       File  permissions  should grant read-only access to the system superuser account ("root"),
       and no access to anyone else.

smtpd_tls_loglevel (default: 0)

       Enable additional Postfix SMTP server logging of TLS activity.  Each  logging  level  also
       includes the information that is logged at a lower logging level.

              0 Disable logging of TLS activity.

              1  Log  only  a  summary message on TLS handshake completion - no logging of client
              certificate trust-chain verification errors if client certificate  verification  is
              not  required.   With  Postfix  2.8  and  earlier,  log  the  summary message, peer
              certificate summary information and unconditionally  log  trust-chain  verification
              errors.

              2 Also log levels during TLS negotiation.

              3 Also log hexadecimal and ASCII dump of TLS negotiation process.

              4 Also log hexadecimal and ASCII dump of complete transmission after STARTTLS.

       Do  not use "smtpd_tls_loglevel = 2" or higher except in case of problems. Use of loglevel
       4 is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_mandatory_ciphers (default: medium)

       The minimum TLS cipher grade that the Postfix SMTP server  will  use  with  mandatory  TLS
       encryption.  The  default  grade  ("medium")  is sufficiently strong that any benefit from
       globally restricting TLS  sessions  to  a  more  stringent  grade  is  likely  negligible,
       especially  given  the  fact  that  many  implementations  still do not offer any stronger
       ("high" grade) ciphers, while those that do, will always  use  "high"  grade  ciphers.  So
       insisting  on  "high"  grade ciphers is generally counter-productive. Allowing "export" or
       "low" ciphers is typically not a good idea, as systems limited to just these  are  limited
       to  obsolete  browsers.  No  known  SMTP  clients fail to support at least one "medium" or
       "high" grade cipher.

       The following cipher grades are supported:

       export Enable "EXPORT" grade or stronger OpenSSL ciphers.  The  underlying  cipherlist  is
              specified  via  the  tls_export_cipherlist  configuration  parameter, which you are
              strongly encouraged to not change.  This choice is insecure and SHOULD NOT be used.

       low    Enable "LOW" grade or  stronger  OpenSSL  ciphers.  The  underlying  cipherlist  is
              specified  via  the  tls_low_cipherlist  configuration  parameter,  which  you  are
              strongly encouraged to not change.  This choice is insecure and SHOULD NOT be used.

       medium Enable "MEDIUM" grade or stronger OpenSSL ciphers.  These  use  128-bit  or  longer
              symmetric  bulk-encryption keys. This is the default minimum strength for mandatory
              TLS   encryption.   The   underlying    cipherlist    is    specified    via    the
              tls_medium_cipherlist configuration parameter, which you are strongly encouraged to
              not change.

       high   Enable only "HIGH" grade OpenSSL ciphers. The underlying  cipherlist  is  specified
              via  the  tls_high_cipherlist  configuration  parameter,  which  you  are  strongly
              encouraged to not change.

       null   Enable only the  "NULL"  OpenSSL  ciphers,  these  provide  authentication  without
              encryption.  This setting is only appropriate in the rare case that all clients are
              prepared to use NULL ciphers (not normally enabled in TLS clients). The  underlying
              cipherlist  is specified via the tls_null_cipherlist configuration parameter, which
              you are strongly encouraged to not change.

       Cipher types listed in  smtpd_tls_mandatory_exclude_ciphers  or  smtpd_tls_exclude_ciphers
       are  excluded from the base definition of the selected cipher grade. See smtpd_tls_ciphers
       for cipher controls that apply to opportunistic TLS.

       The underlying cipherlists for grades other than "null"  include  anonymous  ciphers,  but
       these  are  automatically  filtered out if the server is configured to ask for remote SMTP
       client certificates.  You are very unlikely to need to take any steps to exclude anonymous
       ciphers,  they  are  excluded  automatically  as  required.  If you must exclude anonymous
       ciphers  even   when   Postfix   does   not   need   or   use   peer   certificates,   set
       "smtpd_tls_exclude_ciphers  =  aNULL".  To  exclude  anonymous  ciphers  only  when TLS is
       enforced, set "smtpd_tls_mandatory_exclude_ciphers = aNULL".

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_exclude_ciphers (default: empty)

       Additional list of ciphers or cipher types to exclude from the Postfix SMTP server  cipher
       list  at  mandatory  TLS  security  levels.  This list works in addition to the exclusions
       listed with smtpd_tls_exclude_ciphers (see there for syntax details).

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_protocols (default: !SSLv2, !SSLv3)

       The SSL/TLS protocols accepted by the Postfix SMTP server with mandatory  TLS  encryption.
       If  the  list  is  empty,  the server supports all available SSL/TLS protocol versions.  A
       non-empty value is a list of protocol names separated by  whitespace,  commas  or  colons.
       The supported protocol names are "SSLv2", "SSLv3" and "TLSv1", and are not case sensitive.
       The default value is "!SSLv2, !SSLv3" for Postfix  releases  after  the  middle  of  2015,
       "!SSLv2" for older releases.

       With  Postfix >= 2.5 the parameter syntax was expanded to support protocol exclusions. One
       can explicitly exclude "SSLv2" by setting  "smtpd_tls_mandatory_protocols  =  !SSLv2".  To
       exclude  both  "SSLv2"  and  "SSLv3" set "smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3".
       Listing the protocols to include, rather than protocols to exclude, is supported, but  not
       recommended.  The  exclusion  form  more  closely matches the underlying OpenSSL interface
       semantics.

       Note: As of OpenSSL 1.0.1 two new protocols are defined,  "TLSv1.1"  and  "TLSv1.2".  When
       Postfix  <= 2.5 is linked against OpenSSL 1.0.1 or later, these, or any other new protocol
       versions, cannot be disabled.  The latest patch levels of Postfix >= 2.6, and all versions
       of Postfix >= 2.10 can disable support for "TLSv1.1" or "TLSv1.2".

       Example:

       # Preferred syntax with Postfix >= 2.5:
       smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
       # Legacy syntax:
       smtpd_tls_mandatory_protocols = TLSv1

       This feature is available in Postfix 2.3 and later.

smtpd_tls_protocols (default: !SSLv2, !SSLv3)

       List  of  TLS  protocols  that  the  Postfix  SMTP  server  will  exclude  or include with
       opportunistic TLS encryption. The default value is "!SSLv2, !SSLv3" for  Postfix  releases
       after  the middle of 2015, empty for older releases allowing all protocols to be used with
       opportunistic TLS.  A non-empty value is a list of protocol names separated by whitespace,
       commas  or colons.  The supported protocol names are "SSLv2", "SSLv3" and "TLSv1", and are
       not case sensitive.

       Note: As of OpenSSL 1.0.1 two new protocols are  defined,  "TLSv1.1"  and  "TLSv1.2".  The
       latest  patch  levels  of  Postfix >= 2.6, and all versions of Postfix >= 2.10 can disable
       support for "TLSv1.1" or "TLSv1.2".

       To include a protocol list its name, to exclude it, prefix the name with a "!"  character.
       To exclude SSLv2 for opportunistic TLS set "smtpd_tls_protocols = !SSLv2". To exclude both
       "SSLv2" and "SSLv3" set "smtpd_tls_protocols = !SSLv2,  !SSLv3".  Explicitly  listing  the
       protocols to include, rather than protocols to exclude, is supported, but not recommended.
       The exclusion form more closely matches the underlying OpenSSL interface semantics.

       Example:
       smtpd_tls_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.6 and later.

smtpd_tls_received_header (default: no)

       Request that the Postfix SMTP server produces  Received:   message  headers  that  include
       information  about  the  protocol  and  cipher  used,  as  well  as the remote SMTP client
       CommonName and client certificate issuer CommonName.  This is disabled by default, as  the
       information  may be modified in transit through other mail servers.  Only information that
       was recorded by the final destination can be trusted.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_req_ccert (default: no)

       With mandatory TLS encryption, require a trusted remote SMTP client certificate  in  order
       to allow TLS connections to proceed.  This option implies "smtpd_tls_ask_ccert = yes".

       When  TLS  encryption  is  optional, this setting is ignored with a warning written to the
       mail log.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_security_level (default: empty)

       The SMTP TLS security level for the  Postfix  SMTP  server;  when  a  non-empty  value  is
       specified,  this  overrides  the  obsolete parameters smtpd_use_tls and smtpd_enforce_tls.
       This parameter is ignored with "smtpd_tls_wrappermode = yes".

       Specify one of the following security levels:

       none   TLS will not be used.

       may    Opportunistic TLS: announce STARTTLS support to remote SMTP  clients,  but  do  not
              require that clients use TLS encryption.

       encrypt
              Mandatory  TLS  encryption:  announce  STARTTLS support to remote SMTP clients, and
              require that clients use TLS encryption. According to RFC 2487  this  MUST  NOT  be
              applied  in  case of a publicly-referenced SMTP server. Instead, this option should
              be used only on dedicated servers.

       Note 1: the "fingerprint", "verify" and "secure"  levels  are  not  supported  here.   The
       Postfix  SMTP  server  logs  a  warning and uses "encrypt" instead.  To verify remote SMTP
       client  certificates,  see  TLS_README  for  a  discussion  of  the   smtpd_tls_ask_ccert,
       smtpd_tls_req_ccert, and permit_tls_clientcerts features.

       Note   2:   The   parameter   setting   "smtpd_tls_security_level   =   encrypt"   implies
       "smtpd_tls_auth_only = yes".

       Note 3: when invoked via  "sendmail  -bs",  Postfix  will  never  offer  STARTTLS  due  to
       insufficient privileges to access the server private key. This is intended behavior.

       This feature is available in Postfix 2.3 and later.

smtpd_tls_session_cache_database (default: empty)

       Name  of the file containing the optional Postfix SMTP server TLS session cache. Specify a
       database type that supports enumeration, such as btree  or  sdbm;  there  is  no  need  to
       support  concurrent access.  The file is created if it does not exist. The smtpd(8) daemon
       does not use this parameter directly, rather the cache is implemented  indirectly  in  the
       tlsmgr(8) daemon. This means that per-smtpd-instance master.cf overrides of this parameter
       are not effective. Note, that each of the cache databases supported by  tlsmgr(8)  daemon:
       $smtpd_tls_session_cache_database,  $smtp_tls_session_cache_database (and with Postfix 2.3
       and later $lmtp_tls_session_cache_database), needs to be stored separately. It is  not  at
       this time possible to store multiple caches in a single database.

       Note: dbm databases are not suitable. TLS session objects are too large.

       As of version 2.5, Postfix no longer uses root privileges when opening this file. The file
       should now be stored under the  Postfix-owned  data_directory.  As  a  migration  aid,  an
       attempt  to open the file under a non-Postfix directory is redirected to the Postfix-owned
       data_directory, and a warning is logged.

       As of Postfix 2.11 the preferred mechanism for session resumption is RFC 5077 TLS  session
       tickets,  which don't require server-side storage.  Consequently, for Postfix >= 2.11 this
       parameter should generally be left empty.  TLS session tickets require an OpenSSL  library
       (at  least  version  0.9.8h)  that provides full support for this TLS extension.  See also
       smtpd_tls_session_cache_timeout.

       Example:

       smtpd_tls_session_cache_database = btree:/var/lib/postfix/smtpd_scache

       This feature is available in Postfix 2.2 and later.

smtpd_tls_session_cache_timeout (default: 3600s)

       The expiration time of Postfix SMTP server TLS session cache information. A cache  cleanup
       is   performed   periodically  every  $smtpd_tls_session_cache_timeout  seconds.  As  with
       $smtpd_tls_session_cache_database, this parameter is implemented in the  tlsmgr(8)  daemon
       and therefore per-smtpd-instance master.cf overrides are not possible.

       As  of  Postfix 2.11 this setting cannot exceed 100 days.  If set <= 0, session caching is
       disabled, not just via the database, but also via RFC  5077  TLS  session  tickets,  which
       don't  require  server-side  storage.  If set to a positive value less than 2 minutes, the
       minimum value of 2 minutes is used  instead.   TLS  session  tickets  require  an  OpenSSL
       library (at least version 0.9.8h) that provides full support for this TLS extension.

       This  feature  is  available  in Postfix 2.2 and later, and updated for TLS session ticket
       support in Postfix 2.11.

smtpd_tls_wrappermode (default: no)

       Run the Postfix SMTP server in the non-standard  "wrapper"  mode,  instead  of  using  the
       STARTTLS command.

       If  you  want to support this service, enable a special port in master.cf, and specify "-o
       smtpd_tls_wrappermode=yes" on the SMTP server's command line. Port 465  (smtps)  was  once
       chosen for this purpose.

       This feature is available in Postfix 2.2 and later.

smtpd_upstream_proxy_protocol (default: empty)

       The  name of the proxy protocol used by an optional before-smtpd proxy agent. When a proxy
       agent is used, this protocol conveys  local  and  remote  address  and  port  information.
       Specify "smtpd_upstream_proxy_protocol = haproxy" to enable the haproxy protocol.

       NOTE:   To   use  the  nginx  proxy  with  smtpd(8),  enable  the  XCLIENT  protocol  with
       smtpd_authorized_xclient_hosts. This supports  SASL  authentication  in  the  proxy  agent
       (Postfix 2.9 and later).

       This feature is available in Postfix 2.10 and later.

smtpd_upstream_proxy_timeout (default: 5s)

       The  time  limit  for  the proxy protocol specified with the smtpd_upstream_proxy_protocol
       parameter.

       This feature is available in Postfix 2.10 and later.

smtpd_use_tls (default: no)

       Opportunistic TLS: announce STARTTLS support to remote SMTP clients, but  do  not  require
       that clients use TLS encryption.

       Note:  when  invoked  via  "sendmail  -bs",  Postfix  will  never  offer  STARTTLS  due to
       insufficient privileges to access the server private key. This is intended behavior.

       This feature is available in Postfix 2.2  and  later.  With  Postfix  2.3  and  later  use
       smtpd_tls_security_level instead.

smtputf8_autodetect_classes (default: sendmail, verify)

       Detect  that  a  message  requires SMTPUTF8 support for the specified mail origin classes.
       This is a workaround  to  avoid  chicken-and-egg  problems  during  the  initial  SMTPUTF8
       roll-out  in environments with pre-existing mail flows that contain UTF8. Those mail flows
       should not break because Postfix suddenly refuses to deliver such mail to down-stream MTAs
       that don't announce SMTPUTF8 support.

       The  problem is that Postfix cannot rely solely on the sender's declaration that a message
       requires SMTPUTF8 support, because UTF8 may be introduced  during  local  processing  (for
       example,  the  client  hostname  in  Postfix's  Received:  header,  adding  @$myorigin  or
       .$mydomain to an incomplete address, address rewriting,  alias  expansion,  automatic  BCC
       recipients, local forwarding, and changes made by header checks or Milter applications).

       For  now,  the  default  is  to  enable "SMTPUTF8 required" autodetection only for Postfix
       sendmail command-line submissions and address verification probes.  This may  change  once
       SMTPUTF8  support  achieves  world  domination.   However, sites that add UTF8 content via
       local processing (see above) should autodetect the  need  for  SMTPUTF8  support  for  all
       email.

       Specify one or more of the following:

        sendmail
              Submission with the Postfix sendmail(1) command.

        smtpd Mail received with the smtpd(8) daemon.

        qmqpd Mail received with the qmqpd(8) daemon.

        forward
              Local forwarding or aliasing.  When a message is received with "SMTPUTF8 required",
              then the forwarded (aliased) message always has "SMTPUTF8 required".

        bounce
              Submission by the bounce(8) daemon.  When a  message  is  received  with  "SMTPUTF8
              required", then the delivery status notification always has "SMTPUTF8 required".

        notify
              Postmaster notification from the smtp(8) or smtpd(8) daemon.

        verify
              Address verification probe from the verify(8) daemon.

        all   Enable SMTPUTF8 autodetection for all mail.

       This feature is available in Postfix 3.0 and later.

smtputf8_enable (default: yes)

       Enable  preliminary  SMTPUTF8  support for the protocols described in RFC 6531..6533. This
       requires that Postfix is built to support these protocols.

       This feature is available in Postfix 3.0 and later.

soft_bounce (default: no)

       Safety net to keep mail queued that would otherwise  be  returned  to  the  sender.   This
       parameter  disables  locally-generated bounces, changes the handling of negative responses
       from remote servers, content filters or plugins, and prevents the Postfix SMTP server from
       rejecting  mail permanently by changing 5xx reply codes into 4xx.  However, soft_bounce is
       no cure for address rewriting mistakes or mail routing mistakes.

       Note: "soft_bounce = yes" is in some cases  implemented  by  modifying  server  responses.
       Therefore,  the  response  that  Postfix  logs  may  differ from the response that Postfix
       actually sends or receives.

       Example:

       soft_bounce = yes

stale_lock_time (default: 500s)

       The time after which a stale exclusive mailbox lockfile is  removed.   This  is  used  for
       delivery to file or mailbox.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

stress (default: empty)

       This feature is documented in the STRESS_README document.

       This feature is available in Postfix 2.5 and later.

strict_7bit_headers (default: no)

       Reject mail with 8-bit text in message headers.  This  blocks  mail  from  poorly  written
       applications.

       This  feature should not be enabled on a general purpose mail server, because it is likely
       to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime (default: no)

       Enable both strict_7bit_headers and strict_8bitmime_body.

       This feature should not be enabled on a general purpose mail server, because it is  likely
       to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime_body (default: no)

       Reject  8-bit  message  body  text  without 8-bit MIME content encoding information.  This
       blocks mail from poorly written applications.

       Unfortunately, this also rejects majordomo approval requests  when  the  included  request
       contains  valid  8-bit  MIME  mail,  and  it rejects bounces from mailers that do not MIME
       encapsulate 8-bit content (for example,  bounces  from  qmail  or  from  old  versions  of
       Postfix).

       This  feature should not be enabled on a general purpose mail server, because it is likely
       to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_mailbox_ownership (default: yes)

       Defer delivery when a mailbox file is not owned by its recipient.  The default setting  is
       not backwards compatible.

       This feature is available in Postfix 2.5.3 and later.

strict_mime_encoding_domain (default: no)

       Reject  mail  with  invalid  Content-Transfer-Encoding:  information  for the message/* or
       multipart/* MIME content types.  This blocks mail from poorly written software.

       This feature should not be enabled on a general  purpose  mail  server,  because  it  will
       reject mail after a single violation.

       This feature is available in Postfix 2.0 and later.

strict_rfc821_envelopes (default: no)

       Require  that  addresses received in SMTP MAIL FROM and RCPT TO commands are enclosed with
       <>, and that those addresses do not contain RFC 822 style comments or phrases.  This stops
       mail from poorly written software.

       By  default,  the  Postfix  SMTP  server  accepts  RFC 822 syntax in MAIL FROM and RCPT TO
       addresses.

strict_smtputf8 (default: no)

       Enable stricter enforcement of the SMTPUTF8 protocol. The Postfix SMTP server accepts UTF8
       sender or recipient addresses only when the client requests an SMTPUTF8 mail transaction.

       This feature is available in Postfix 3.0 and later.

sun_mailtool_compatibility (default: no)

       Obsolete  SUN  mailtool  compatibility  feature.  Instead,  use  "mailbox_delivery_lock  =
       dotlock".

swap_bangpath (default: yes)

       Enable the rewriting of "site!user" into "user@site".  This is necessary if  your  machine
       is connected to UUCP networks.  It is enabled by default.

       Note:  with Postfix version 2.2, message header address rewriting happens only when one of
       the following conditions is true:

       ·      The message is received with the Postfix sendmail(1) command,

       ·      The   message   is    received    from    a    network    client    that    matches
              $local_header_rewrite_clients,

       ·      The  message  is  received  from  the network, and the remote_header_rewrite_domain
              parameter specifies a non-empty value.

       To get the behavior before Postfix version 2.2,  specify  "local_header_rewrite_clients  =
       static:all".

       Example:

       swap_bangpath = no

syslog_facility (default: mail)

       The  syslog  facility of Postfix logging. Specify a facility as defined in syslog.conf(5).
       The default facility is "mail".

       Warning: a non-default syslog_facility setting takes effect only after a  Postfix  process
       has  completed  initialization.   Errors during process initialization will be logged with
       the default facility.  Examples are errors while parsing the command line  arguments,  and
       errors while accessing the Postfix main.cf configuration file.

syslog_name (default: see postconf -d output)

       A  prefix  that  is prepended to the process name in syslog records, so that, for example,
       "smtpd" becomes "prefix/smtpd".

       Warning: a non-default syslog_name setting takes effect only after a Postfix  process  has
       completed  initialization.  Errors  during  process initialization will be logged with the
       default name. Examples are errors while parsing the command  line  arguments,  and  errors
       while accessing the Postfix main.cf configuration file.

tcp_windowsize (default: 0)

       An optional workaround for routers that break TCP window scaling.  Specify a value > 0 and
       < 65536 to enable this feature.  With  Postfix  TCP  servers  (smtpd(8),  qmqpd(8)),  this
       feature is implemented by the Postfix master(8) daemon.

       To change this parameter without stopping Postfix, you need to first terminate all Postfix
       TCP servers:

           # postconf -e master_service_disable=inet
           # postfix reload

       This immediately terminates all processes that  accept  network  connections.   Next,  you
       enable Postfix TCP servers with the updated tcp_windowsize setting:

           # postconf -e tcp_windowsize=65535 master_service_disable=
           # postfix reload

       If you skip these steps with a running Postfix system, then the tcp_windowsize change will
       work only for Postfix TCP clients (smtp(8), lmtp(8)).

       This feature is available in Postfix 2.6 and later.

tls_append_default_CA (default: no)

       Append the system-supplied  default  Certification  Authority  certificates  to  the  ones
       specified  with  *_tls_CApath or *_tls_CAfile.  The default is "no"; this prevents Postfix
       from  trusting  third-party  certificates  and   giving   them   relay   permission   with
       permit_tls_all_clientcerts.

       This  feature  is  available  in  Postfix 2.4.15, 2.5.11, 2.6.8, 2.7.2 and later versions.
       Specify "tls_append_default_CA = yes"  for  backwards  compatibility,  to  avoid  breaking
       certificate verification with sites that don't use permit_tls_all_clientcerts.

tls_daemon_random_bytes (default: 32)

       The  number  of  pseudo-random bytes that an smtp(8) or smtpd(8) process requests from the
       tlsmgr(8) server in order to seed its internal pseudo random number generator (PRNG).  The
       default  of  32  bytes  (equivalent  to  256  bits) is sufficient to generate a 128bit (or
       168bit) session key.

       This feature is available in Postfix 2.2 and later.

tls_dane_digest_agility (default: on)

       Configure RFC7671 DANE TLSA digest algorithm agility.  Do not change this setting from its
       default value.

       See Section 8 of RFC7671 for correct key rotation procedures.

       This  feature is available in Postfix 2.11 through 3.1.  Postfix 3.2 and later ignore this
       configuration parameter and behave as though it were set to "on".

tls_dane_digests (default: sha512 sha256)

       DANE TLSA (RFC 6698, RFC 7671, RFC 7672) resource-record "matching type" digest algorithms
       in  descending  preference  order.   All the specified algorithms must be supported by the
       underlying OpenSSL library, otherwise the Postfix SMTP client will not support  DANE  TLSA
       security.

       Specify  a  list  of digest names separated by commas and/or whitespace.  Each digest name
       may be followed by an optional "=<number>" suffix.  For example, "sha512" may  instead  be
       specified as "sha512=2" and "sha256" may instead be specified as "sha256=1".  The optional
       number                 must                 match                  the                  <a
       href="https://www.iana.org/assignments/dane-parameters/dane-parameters.xhtml#matching-types"
       >IANA assigned TLSA matching type number the algorithm in question.   Postfix  will  check
       this  constraint  for  the algorithms it knows about.  Additional matching type algorithms
       registered with IANA can be added with explicit numbers provided  they  are  supported  by
       OpenSSL.

       Invalid  list  elements are logged with a warning and disable DANE support.  TLSA RRs that
       specify digests not included in the list are ignored with a warning.

       Note: It is unwise to omit sha256 from the digest list.  This digest algorithm is the only
       mandatory to implement digest algorithm in RFC 6698, and many servers are expected publish
       TLSA records with just sha256 digests.  Unless one of the standard  digests  is  seriously
       compromised  and  servers  have had ample time to update their TLSA records you should not
       omit any standard digests, just arrange them in order from strongest to weakest.

       This feature is available in Postfix 2.11 and later.

tls_dane_trust_anchor_digest_enable (default: yes)

       Enable support for RFC 6698 (DANE TLSA) DNS records that contain digests of  trust-anchors
       with certificate usage "2".  Do not change this setting from its default value.

       This  feature  is available in Postfix 2.11 through 3.1.  It has been withdrawn in Postfix
       3.2, as trust-anchor TLSA records  are  now  widely  used  and  have  proved  sufficiently
       reliable.  Postfix 3.2 and later ignore this configuration parameter and behaves as though
       it were set to "yes".

tls_disable_workarounds (default: see postconf -d output)

       List or bit-mask of OpenSSL bug work-arounds to disable.

       The OpenSSL toolkit includes a set of  work-arounds  for  buggy  SSL/TLS  implementations.
       Applications,  such  as  Postfix,  that  want to maximize interoperability ask the OpenSSL
       library to enable the full set of recommended work-arounds.

       From time to time, it is discovered that a  work-around  creates  a  security  issue,  and
       should  no  longer be used. If upgrading OpenSSL to a fixed version is not an option or an
       upgrade is not available in a timely manner, or in  closed  environments  where  no  buggy
       clients  or  servers  exist,  it  may be appropriate to disable some or all of the OpenSSL
       interoperability work-arounds. This parameter specifies which bug work-arounds to disable.

       If the value of the parameter is a hexadecimal long integer starting with  "0x",  the  bug
       work-arounds  corresponding  to  the  bits  specified  in  its  value are removed from the
       SSL_OP_ALL work-around bit-mask (see openssl/ssl.h and  SSL_CTX_set_options(3)).  You  can
       specify  more  bits  than  are  present in SSL_OP_ALL, excess bits are ignored. Specifying
       0xFFFFFFFF disables all bug-workarounds on a 32-bit system. This should also be sufficient
       on  64-bit systems, until OpenSSL abandons support for 32-bit systems and starts using the
       high 32 bits of a 64-bit bug-workaround mask.

       Otherwise, the parameter is a white-space or comma separated list of  specific  named  bug
       work-arounds chosen from the list below. It is possible that your OpenSSL version includes
       new bug work-arounds added after your Postfix source code was last updated, in  that  case
       you can only disable one of these via the hexadecimal syntax above.

       MICROSOFT_SESS_ID_BUG
              See SSL_CTX_set_options(3)

       NETSCAPE_CHALLENGE_BUG
              See SSL_CTX_set_options(3)

       LEGACY_SERVER_CONNECT
              See SSL_CTX_set_options(3)

       NETSCAPE_REUSE_CIPHER_CHANGE_BUG
              also  aliased  as  CVE-2010-4180.  Postfix 2.8 disables this work-around by default
              with OpenSSL versions that may predate the fix. Fixed in OpenSSL 0.9.8q and OpenSSL
              1.0.0c.

       SSLREF2_REUSE_CERT_TYPE_BUG
              See SSL_CTX_set_options(3)

       MICROSOFT_BIG_SSLV3_BUFFER
              See SSL_CTX_set_options(3)

       MSIE_SSLV2_RSA_PADDING
              also  aliased  as  CVE-2005-2969.  Postfix 2.8 disables this work-around by default
              with OpenSSL versions that may predate the fix. Fixed in OpenSSL 0.9.7h and OpenSSL
              0.9.8a.

       SSLEAY_080_CLIENT_DH_BUG
              See SSL_CTX_set_options(3)

       TLS_D5_BUG
              See SSL_CTX_set_options(3)

       TLS_BLOCK_PADDING_BUG
              See SSL_CTX_set_options(3)

       TLS_ROLLBACK_BUG
              See  SSL_CTX_set_options(3).   This  is disabled in OpenSSL 0.9.7 and later. Nobody
              should still be using 0.9.6!

       DONT_INSERT_EMPTY_FRAGMENTS
              See SSL_CTX_set_options(3)

       CRYPTOPRO_TLSEXT_BUG
              New with GOST support in OpenSSL 1.0.0.

       This feature is available in Postfix 2.8 and later.

tls_eecdh_auto_curves (default: see postconf -d output)

       The prioritized list of elliptic curves supported by the Postfix SMTP client  and  server.
       These curves are used by the Postfix SMTP server when "smtpd_tls_eecdh_grade = auto".  The
       selected curves must be implemented by OpenSSL and be standardized for  use  in  TLS  (RFC
       4492  or  its  imminent  successor).   It  is  unwise  to list only "bleeding-edge" curves
       supported by a small subset of clients.  The default list is suitable for most users.

       Postfix skips curve names that are unknown to OpenSSL, or  that  are  known  but  not  yet
       implemented.   This  makes  it  possible to "anticipate" support for curves that should be
       used once they become available.  In particular, in some OpenSSL  versions,  the  new  RFC
       8031  curves "X25519" and "X448" may be known by name, but ECDH support for either or both
       may be missing.  These curves may appear in the default  value  of  this  parameter,  even
       though they'll only be usable with later versions of OpenSSL.

       This  feature  is  available in Postfix 3.2 and later, when it is compiled and linked with
       OpenSSL 1.0.2 or later on platforms where EC algorithms have  not  been  disabled  by  the
       vendor.

tls_eecdh_strong_curve (default: prime256v1)

       The  elliptic curve used by the Postfix SMTP server for sensibly strong ephemeral ECDH key
       exchange. This curve is used by the Postfix  SMTP  server  when  "smtpd_tls_eecdh_grade  =
       strong".  The  phrase "sensibly strong" means approximately 128-bit security based on best
       known attacks. The  selected  curve  must  be  implemented  by  OpenSSL  (as  reported  by
       ecparam(1)  with  the  "-list_curves"  option)  and be one of the curves listed in Section
       5.1.1 of RFC 4492. You should not generally  change  this  setting.   Remote  SMTP  client
       implementations  must  support  this  curve  for  EECDH key exchange to take place.  It is
       unwise to choose an "bleeding-edge" curve supported by only a small subset of clients.

       The default "strong" curve is rated in NSA  Suite  B  for  information  classified  up  to
       SECRET.

       Note:  elliptic  curve  names  are  poorly  standardized;  different  standards groups are
       assigning different names to the same underlying curves.  The curve with  the  X9.62  name
       "prime256v1" is also known under the SECG name "secp256r1", but OpenSSL does not recognize
       the latter name.

       If you want to take maximal advantage of  ciphers  that  offer  forward  secrecy  see  the
       Getting  started  section  of  FORWARD_SECRECY_README.   The  full  document  conveniently
       presents all information about Postfix "perfect" forward secrecy  support  in  one  place:
       what  forward  secrecy  is,  how  to  tweak  settings, and what you can expect to see when
       Postfix uses ciphers with forward secrecy.

       This feature is available in Postfix 2.6 and later, when it is compiled  and  linked  with
       OpenSSL  1.0.0  or  later  on  platforms where EC algorithms have not been disabled by the
       vendor.

tls_eecdh_ultra_curve (default: secp384r1)

       The elliptic curve used by the Postfix SMTP server for maximally strong ephemeral ECDH key
       exchange.  This  curve  is  used  by the Postfix SMTP server when "smtpd_tls_eecdh_grade =
       ultra". The phrase "maximally strong" means approximately 192-bit security based  on  best
       known  attacks.   This additional strength comes at a significant computational cost, most
       users should instead set "smtpd_tls_eecdh_grade = strong".  The  selected  curve  must  be
       implemented  by  OpenSSL (as reported by ecparam(1) with the "-list_curves" option) and be
       one of the curves listed in Section 5.1.1 of RFC 4492. You  should  not  generally  change
       this setting.

       This  default  "ultra"  curve is rated in NSA Suite B for information classified up to TOP
       SECRET.

       If you want to take maximal advantage of  ciphers  that  offer  forward  secrecy  see  the
       Getting  started  section  of  FORWARD_SECRECY_README.   The  full  document  conveniently
       presents all information about Postfix "perfect" forward secrecy  support  in  one  place:
       what  forward  secrecy  is,  how  to  tweak  settings, and what you can expect to see when
       Postfix uses ciphers with forward secrecy.

       This feature is available in Postfix 2.6 and later, when it is compiled  and  linked  with
       OpenSSL  1.0.0  or  later  on  platforms where EC algorithms have not been disabled by the
       vendor.

tls_export_cipherlist (default: see postconf -d output)

       The OpenSSL cipherlist for "export" or higher grade ciphers. This defines the  meaning  of
       the  "export" setting in smtpd_tls_ciphers, smtpd_tls_mandatory_ciphers, smtp_tls_ciphers,
       smtp_tls_mandatory_ciphers,  lmtp_tls_ciphers,   and   lmtp_tls_mandatory_ciphers.    With
       Postfix  releases  before  the  middle  of  2015  this  is  the default cipherlist for the
       opportunistic ("may") TLS client security level and also the default  cipherlist  for  the
       SMTP server. You are strongly encouraged to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_high_cipherlist (default: see postconf -d output)

       The  OpenSSL  cipherlist  for "high" grade ciphers. This defines the meaning of the "high"
       setting    in    smtpd_tls_ciphers,     smtpd_tls_mandatory_ciphers,     smtp_tls_ciphers,
       smtp_tls_mandatory_ciphers,  lmtp_tls_ciphers,  and  lmtp_tls_mandatory_ciphers.  You  are
       strongly encouraged to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_legacy_public_key_fingerprints (default: no)

       A temporary migration aid for sites that  use  certificate  public-key  fingerprints  with
       Postfix  2.9.0..2.9.5,  which  use an incorrect algorithm. This parameter has no effect on
       the certificate fingerprint support that is available since Postfix 2.2.

       Specify "tls_legacy_public_key_fingerprints = yes" temporarily, pending a  migration  from
       configuration  files  with  incorrect  Postfix  2.9.0..2.9.5 certificate public-key finger
       prints, to the correct fingerprints used by Postfix  2.9.6  and  later.   To  compute  the
       correct certificate public-key fingerprints, see TLS_README.

       This feature is available in Postfix 2.9.6 and later.

tls_low_cipherlist (default: see postconf -d output)

       The  OpenSSL cipherlist for "low" or higher grade ciphers. This defines the meaning of the
       "low"  setting  in   smtpd_tls_ciphers,   smtpd_tls_mandatory_ciphers,   smtp_tls_ciphers,
       smtp_tls_mandatory_ciphers,  lmtp_tls_ciphers,  and  lmtp_tls_mandatory_ciphers.  You  are
       strongly encouraged to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_medium_cipherlist (default: see postconf -d output)

       The OpenSSL cipherlist for "medium" or higher grade ciphers. This defines the  meaning  of
       the  "medium" setting in smtpd_tls_ciphers, smtpd_tls_mandatory_ciphers, smtp_tls_ciphers,
       smtp_tls_mandatory_ciphers, lmtp_tls_ciphers, and lmtp_tls_mandatory_ciphers.  This is the
       default  cipherlist for mandatory TLS encryption in the TLS client (with anonymous ciphers
       disabled when  verifying  server  certificates).   This  is  the  default  cipherlist  for
       opportunistic  TLS  with  Postfix  releases  after  the  middle of 2015.  You are strongly
       encouraged to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_null_cipherlist (default: eNULL:!aNULL)

       The OpenSSL cipherlist for  "NULL"  grade  ciphers  that  provide  authentication  without
       encryption. This defines the meaning of the "null" setting in smtpd_mandatory_tls_ciphers,
       smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers.  You are strongly encouraged to
       not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_preempt_cipherlist (default: no)

       With SSLv3 and later, use the Postfix SMTP server's cipher preference order instead of the
       remote client's cipher preference order.

       By default, the OpenSSL server selects the client's most preferred cipher that the  server
       supports.  With  SSLv3 and later, the server may choose its own most preferred cipher that
       is supported (offered) by the  client.  Setting  "tls_preempt_cipherlist  =  yes"  enables
       server cipher preferences.

       While server cipher selection may in some cases lead to a more secure or performant cipher
       choice, there is some risk of interoperability issues. In the past, some SSL clients  have
       listed lower priority ciphers that they did not implement correctly. If the server chooses
       a cipher that the client prefers less, it may select a cipher whose client  implementation
       is   flawed.   Most   notably   Windows   2003  Microsoft  Exchange  servers  have  flawed
       implementations of DES-CBC3-SHA, which OpenSSL considers stronger than RC4-SHA.   Enabling
       server  cipher-suite  selection  may  create  interoperability  issues  with  Windows 2003
       Microsoft Exchange clients.

       This feature is available in Postfix 2.8 and later, in combination with OpenSSL 0.9.7  and
       later.

tls_random_bytes (default: 32)

       The  number  of  bytes  that  tlsmgr(8) reads from $tls_random_source when (re)seeding the
       in-memory pseudo random number generator (PRNG) pool. The default of 32 bytes  (256  bits)
       is good enough for 128bit symmetric keys.  If using EGD or a device file, a maximum of 255
       bytes is read.

       This feature is available in Postfix 2.2 and later.

tls_random_exchange_name (default: see postconf -d output)

       Name of the pseudo random number  generator  (PRNG)  state  file  that  is  maintained  by
       tlsmgr(8).  The  file  is  created when it does not exist, and its length is fixed at 1024
       bytes.

       As of version 2.5, Postfix no longer uses root privileges when opening this file, and  the
       default    file    location    was    changed    from   ${config_directory}/prng_exch   to
       ${data_directory}/prng_exch.  As a migration aid, an attempt to  open  the  file  under  a
       non-Postfix  directory is redirected to the Postfix-owned data_directory, and a warning is
       logged.

       This feature is available in Postfix 2.2 and later.

tls_random_prng_update_period (default: 3600s)

       The time between attempts by tlsmgr(8) to save the  state  of  the  pseudo  random  number
       generator (PRNG) to the file specified with $tls_random_exchange_name.

       This feature is available in Postfix 2.2 and later.

tls_random_reseed_period (default: 3600s)

       The  maximal  time  between  attempts  by tlsmgr(8) to re-seed the in-memory pseudo random
       number generator (PRNG) pool from external sources.  The actual  time  between  re-seeding
       attempts is calculated using the PRNG, and is between 0 and the time specified.

       This feature is available in Postfix 2.2 and later.

tls_random_source (default: see postconf -d output)

       The  external  entropy  source  for the in-memory tlsmgr(8) pseudo random number generator
       (PRNG) pool. Be sure to specify a non-blocking source.  If this source is  not  a  regular
       file,  the  entropy  source  type must be prepended:  egd:/path/to/egd_socket for a source
       with EGD compatible socket interface, or dev:/path/to/device for a device file.

       Note: on OpenBSD systems specify /dev/arandom when /dev/urandom gives timeout errors.

       This feature is available in Postfix 2.2 and later.

tls_session_ticket_cipher (default: Postfix >= 3.0: aes-256-cbc, Postfix < 3.0: aes-128-cbc)

       Algorithm used to encrypt RFC5077 TLS session tickets.  This algorithm must use CBC  mode,
       have  a  128-bit  block  size,  and  must have a key length between 128 and 256 bits.  The
       default is aes-256-cbc.  Overriding  the  default  to  choose  a  different  algorithm  is
       discouraged.

       Setting  this  parameter empty disables session ticket support in the Postfix SMTP server.
       Another way to disable session ticket support is via the tls_ssl_options parameter.

       This feature is available in Postfix 3.0 and later.

tls_ssl_options (default: empty)

       List or bit-mask of OpenSSL options to enable.

       The OpenSSL toolkit provides a set of options that applications can  enable  to  tune  the
       OpenSSL  behavior.   Some of these work around bugs in other implementations and are on by
       default.  You can use the tls_disable_workarounds parameter to selectively disable some or
       all   of   the   bug   work-arounds,   making   OpenSSL   more   strict  at  the  cost  of
       non-interoperability with SSL clients or servers that exhibit the bugs.

       Other options are off by default, and typically enable or disable features rather than bug
       work-arounds.   These may be turned on (with care) via the tls_ssl_options parameter.  The
       value is a white-space or comma separated list of  named  options  chosen  from  the  list
       below.  The names are not case-sensitive, you can use lower-case if you prefer.  The upper
       case values below match the corresponding macro name in the ssl.h  header  file  with  the
       SSL_OP_  prefix  removed.   It  is possible that your OpenSSL version includes new options
       added after your Postfix source code was last updated, in that case you  can  only  enable
       one of these via the hexadecimal syntax below.

       You  should  only  enable  features  via the hexadecimal mask when the need to control the
       feature is critical (to deal with  a  new  vulnerability  or  a  serious  interoperability
       problem).  Postfix DOES NOT promise backwards compatible behavior with respect to the mask
       bits.  A feature enabled via the mask in one release may be enabled by other  means  in  a
       later  release,  and the mask bit will then be ignored.  Therefore, use of the hexadecimal
       mask is only a temporary measure until a new Postfix or OpenSSL release provides a  better
       solution.

       If  the  value  of  the  parameter  is  a hexadecimal long integer starting with "0x", the
       options corresponding to the bits specified in its value are  enabled  (see  openssl/ssl.h
       and  SSL_CTX_set_options(3)).  You can only enable options not already controlled by other
       Postfix settings.  For example, you cannot  disable  protocols  or  enable  server  cipher
       preference.   Do  not  attempt  to  turn  all  features  by specifying 0xFFFFFFFF, this is
       unlikely to be a good idea.

       LEGACY_SERVER_CONNECT
              See SSL_CTX_set_options(3).

       NO_TICKET
              See SSL_CTX_set_options(3).

       NO_COMPRESSION
              Disable SSL compression even if supported by the OpenSSL library.   Compression  is
              CPU-intensive, and compression before encryption does not always improve security.

       This feature is available in Postfix 2.11 and later.

tls_wildcard_matches_multiple_labels (default: yes)

       Match multiple DNS labels with "*" in wildcard certificates.

       Some  mail  service  providers prepend the customer domain name to a base domain for which
       they have a wildcard TLS certificate.  For example, the MX records for example.com  hosted
       by example.net may be:

           example.com. IN MX 0 example.com.mx1.example.net.
           example.com. IN MX 0 example.com.mx2.example.net.

       and the TLS certificate may be for "*.example.net". The "*" then corresponds with multiple
       labels in the mail server  domain  name.   While  multi-label  wildcards  are  not  widely
       supported,  and  are  not  blessed  by  any  standard,  there  is  little  to be gained by
       disallowing their use in this context.

       Notes:

       ·      In a certificate name, the "*" is special only when it is used as the first label.

       ·      While Postfix (2.11 or later) can match "*" with multiple domain name labels, other
              implementations likely will not.

       ·      Earlier  Postfix implementations behave as if "tls_wildcard_matches_multiple_labels
              = no".

       This feature is available in Postfix 2.11 and later.

tlsmgr_service_name (default: tlsmgr)

       The name of the tlsmgr(8) service entry in master.cf. This service maintains  TLS  session
       caches and other information in support of TLS.

       This feature is available in Postfix 2.11 and later.

tlsproxy_enforce_tls (default: $smtpd_enforce_tls)

       Mandatory  TLS: announce STARTTLS support to remote SMTP clients, and require that clients
       use TLS encryption. See smtpd_enforce_tls for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_service_name (default: tlsproxy)

       The name of the tlsproxy(8) service entry in master.cf. This  service  performs  plaintext
       <=> TLS ciphertext conversion.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_CAfile (default: $smtpd_tls_CAfile)

       A  file  containing (PEM format) CA certificates of root CAs trusted to sign either remote
       SMTP client certificates  or  intermediate  CA  certificates.   See  smtpd_tls_CAfile  for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_CApath (default: $smtpd_tls_CApath)

       A  directory  containing  (PEM  format) CA certificates of root CAs trusted to sign either
       remote SMTP client certificates or intermediate CA certificates. See smtpd_tls_CApath  for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_always_issue_session_ids (default: $smtpd_tls_always_issue_session_ids)

       Force  the  Postfix  tlsproxy(8)  server  to issue a TLS session id, even when TLS session
       caching is turned off. See smtpd_tls_always_issue_session_ids for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_ask_ccert (default: $smtpd_tls_ask_ccert)

       Ask a remote SMTP client for a client certificate.  See  smtpd_tls_ask_ccert  for  further
       details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_ccert_verifydepth (default: $smtpd_tls_ccert_verifydepth)

       The  verification depth for remote SMTP client certificates. A depth of 1 is sufficient if
       the issuing CA is listed in a local CA file. See smtpd_tls_ccert_verifydepth  for  further
       details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_cert_file (default: $smtpd_tls_cert_file)

       File  with  the  Postfix  tlsproxy(8) server RSA certificate in PEM format.  This file may
       also contain the Postfix tlsproxy(8) server private RSA key.  See smtpd_tls_cert_file  for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_ciphers (default: $smtpd_tls_ciphers)

       The  minimum  TLS  cipher  grade  that  the  Postfix  tlsproxy(8)  server  will  use  with
       opportunistic TLS encryption. See smtpd_tls_ciphers for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dcert_file (default: $smtpd_tls_dcert_file)

       File with the Postfix tlsproxy(8) server DSA certificate in PEM  format.   This  file  may
       also contain the Postfix tlsproxy(8) server private DSA key.  See smtpd_tls_dcert_file for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dh1024_param_file (default: $smtpd_tls_dh1024_param_file)

       File with DH parameters that the Postfix tlsproxy(8) server should use with non-export EDH
       ciphers. See smtpd_tls_dh1024_param_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dh512_param_file (default: $smtpd_tls_dh512_param_file)

       File  with  DH parameters that the Postfix tlsproxy(8) server should use with export-grade
       EDH ciphers. See smtpd_tls_dh512_param_file for further details.  The default SMTP  server
       cipher  grade  is "medium" with Postfix releases after the middle of 2015, and as a result
       export-grade cipher suites are by default not used.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dkey_file (default: $smtpd_tls_dkey_file)

       File with the Postfix tlsproxy(8) server DSA private key in PEM format.  This file may  be
       combined  with  the  Postfix  tlsproxy(8)  server  DSA  certificate  file  specified  with
       $smtpd_tls_dcert_file.  See smtpd_tls_dkey_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eccert_file (default: $smtpd_tls_eccert_file)

       File with the Postfix tlsproxy(8) server ECDSA certificate in PEM format.  This  file  may
       also  contain the Postfix tlsproxy(8) server private ECDSA key.  See smtpd_tls_eccert_file
       for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eckey_file (default: $smtpd_tls_eckey_file)

       File with the Postfix tlsproxy(8) server ECDSA private key in PEM format.  This  file  may
       be  combined  with  the  Postfix  tlsproxy(8) server ECDSA certificate file specified with
       $smtpd_tls_eccert_file.  See smtpd_tls_eckey_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eecdh_grade (default: $smtpd_tls_eecdh_grade)

       The Postfix tlsproxy(8) server security grade for ephemeral elliptic-curve  Diffie-Hellman
       (EECDH) key exchange. See smtpd_tls_eecdh_grade for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_exclude_ciphers (default: $smtpd_tls_exclude_ciphers)

       List  of ciphers or cipher types to exclude from the tlsproxy(8) server cipher list at all
       TLS security levels. See smtpd_tls_exclude_ciphers for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_fingerprint_digest (default: $smtpd_tls_fingerprint_digest)

       The message digest algorithm to construct remote SMTP client-certificate fingerprints. See
       smtpd_tls_fingerprint_digest for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_key_file (default: $smtpd_tls_key_file)

       File  with the Postfix tlsproxy(8) server RSA private key in PEM format.  This file may be
       combined  with  the  Postfix  tlsproxy(8)  server  RSA  certificate  file  specified  with
       $smtpd_tls_cert_file.  See smtpd_tls_key_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_loglevel (default: $smtpd_tls_loglevel)

       Enable  additional Postfix tlsproxy(8) server logging of TLS activity.  Each logging level
       also  includes  the  information  that  is  logged  at  a   lower   logging   level.   See
       smtpd_tls_loglevel for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_ciphers (default: $smtpd_tls_mandatory_ciphers)

       The  minimum  TLS cipher grade that the Postfix tlsproxy(8) server will use with mandatory
       TLS encryption. See smtpd_tls_mandatory_ciphers for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_exclude_ciphers (default: $smtpd_tls_mandatory_exclude_ciphers)

       Additional list of ciphers or cipher types to exclude from the tlsproxy(8)  server  cipher
       list  at  mandatory  TLS  security  levels.   See  smtpd_tls_mandatory_exclude_ciphers for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_protocols (default: $smtpd_tls_mandatory_protocols)

       The SSL/TLS protocols accepted by  the  Postfix  tlsproxy(8)  server  with  mandatory  TLS
       encryption.  If  the  list  is  empty,  the server supports all available SSL/TLS protocol
       versions.  See smtpd_tls_mandatory_protocols for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_protocols (default: $smtpd_tls_protocols)

       List of TLS protocols that the Postfix tlsproxy(8) server will  exclude  or  include  with
       opportunistic TLS encryption. See smtpd_tls_protocols for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_req_ccert (default: $smtpd_tls_req_ccert)

       With  mandatory  TLS encryption, require a trusted remote SMTP client certificate in order
       to allow TLS connections to proceed.  See smtpd_tls_req_ccert for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_security_level (default: $smtpd_tls_security_level)

       The SMTP TLS security level for the Postfix tlsproxy(8) server; when a non-empty value  is
       specified, this overrides the obsolete parameters smtpd_use_tls and smtpd_enforce_tls. See
       smtpd_tls_security_level for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_session_cache_timeout (default: $smtpd_tls_session_cache_timeout)

       Obsolete expiration time of Postfix tlsproxy(8)  server  TLS  session  cache  information.
       Since  the  cache  is  shared  with  smtpd(8)  and managed by tlsmgr(8), there is only one
       expiration  time  for  the  SMTP  server  cache  shared  by  all  three  services,  namely
       smtpd_tls_session_cache_timeout.

       This feature is available in Postfix 2.8 and later.

tlsproxy_use_tls (default: $smtpd_use_tls)

       Opportunistic  TLS:  announce  STARTTLS support to remote SMTP clients, but do not require
       that clients use TLS encryption. See smtpd_use_tls for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_watchdog_timeout (default: 10s)

       How much time a tlsproxy(8) process may take to process local or remote I/O before  it  is
       terminated  by  a  built-in  watchdog  timer.   This  is  a safety mechanism that prevents
       tlsproxy(8) from becoming non-responsive due to a bug  in  Postfix  itself  or  in  system
       software.  To avoid false alarms and unnecessary cache corruption this limit cannot be set
       under 10s.

       Specify a non-zero time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time  unit).  Time units: s (seconds), m (minutes), h (hours), d (days), w
       (weeks).

       This feature is available in Postfix 2.8.

trace_service_name (default: trace)

       The name of the trace service. This service is implemented by  the  bounce(8)  daemon  and
       maintains  a  record  of  mail deliveries and produces a mail delivery report when verbose
       delivery is requested with "sendmail -v".

       This feature is available in Postfix 2.1 and later.

transport_delivery_slot_cost (default: $default_delivery_slot_cost)

       A transport-specific override for the default_delivery_slot_cost  parameter  value,  where
       transport is the master.cf name of the message delivery transport.

       Note:  transport_delivery_slot_cost  parameters  will  not  show  up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is  a  combination  of  a  master.cf  service  name  and  a built-in suffix (in this case:
       "_delivery_slot_cost").

transport_delivery_slot_discount (default: $default_delivery_slot_discount)

       A transport-specific override  for  the  default_delivery_slot_discount  parameter  value,
       where transport is the master.cf name of the message delivery transport.

       Note:  transport_delivery_slot_discount  parameters will not show up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is  a  combination  of  a  master.cf  service  name  and  a built-in suffix (in this case:
       "_delivery_slot_discount").

transport_delivery_slot_loan (default: $default_delivery_slot_loan)

       A transport-specific override for the default_delivery_slot_loan  parameter  value,  where
       transport is the master.cf name of the message delivery transport.

       Note:  transport_delivery_slot_loan  parameters  will  not  show  up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is  a  combination  of  a  master.cf  service  name  and  a built-in suffix (in this case:
       "_delivery_slot_loan").

transport_destination_concurrency_failed_cohort_limit (default:

       $default_destination_concurrency_failed_cohort_limit)
       A  transport-specific override for the default_destination_concurrency_failed_cohort_limit
       parameter value, where transport is the master.cf name of the message delivery transport.

       Note: some transport_destination_concurrency_failed_cohort_limit parameters will not  show
       up  in  "postconf"  command output before Postfix version 2.9.  This limitation applies to
       many parameters whose name is a combination of a master.cf service  name  and  a  built-in
       suffix (in this case: "_destination_concurrency_failed_cohort_limit").

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_limit (default: $default_destination_concurrency_limit)

       A  transport-specific  override  for  the  default_destination_concurrency_limit parameter
       value, where transport is the master.cf name of the message delivery transport.

       Note:  some  transport_destination_concurrency_limit  parameters  will  not  show  up   in
       "postconf"  command  output  before  Postfix version 2.9.  This limitation applies to many
       parameters whose name is a combination of a master.cf service name and a  built-in  suffix
       (in this case: "_destination_concurrency_limit").

transport_destination_concurrency_negative_feedback (default:

       $default_destination_concurrency_negative_feedback)
       A transport-specific override  for  the  default_destination_concurrency_negative_feedback
       parameter value, where transport is the master.cf name of the message delivery transport.

       Note: some transport_destination_concurrency_negative_feedback parameters will not show up
       in "postconf" command output before Postfix version 2.9.  This limitation applies to  many
       parameters  whose  name is a combination of a master.cf service name and a built-in suffix
       (in this case: "_destination_concurrency_negative_feedback").

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_positive_feedback (default:

       $default_destination_concurrency_positive_feedback)
       A  transport-specific  override  for the default_destination_concurrency_positive_feedback
       parameter value, where transport is the master.cf name of the message delivery transport.

       Note: some transport_destination_concurrency_positive_feedback parameters will not show up
       in  "postconf" command output before Postfix version 2.9.  This limitation applies to many
       parameters whose name is a combination of a master.cf service name and a  built-in  suffix
       (in this case: "_destination_concurrency_positive_feedback").

       This feature is available in Postfix 2.5 and later.

transport_destination_rate_delay (default: $default_destination_rate_delay)

       A  transport-specific  override  for  the  default_destination_rate_delay parameter value,
       where transport is the master.cf name of the message delivery transport.

       Note: some transport_destination_rate_delay parameters will  not  show  up  in  "postconf"
       command  output  before  Postfix  version 2.9.  This limitation applies to many parameters
       whose name is a combination of a master.cf service name and a  built-in  suffix  (in  this
       case: "_destination_rate_delay").

       This feature is available in Postfix 2.5 and later.

transport_destination_recipient_limit (default: $default_destination_recipient_limit)

       A transport-specific override for the default_destination_recipient_limit parameter value,
       where transport is the master.cf name of the message delivery transport.

       Note: some transport_destination_recipient_limit parameters will not show up in "postconf"
       command  output  before  Postfix  version 2.9.  This limitation applies to many parameters
       whose name is a combination of a master.cf service name and a  built-in  suffix  (in  this
       case: "_destination_recipient_limit").

transport_extra_recipient_limit (default: $default_extra_recipient_limit)

       A transport-specific override for the default_extra_recipient_limit parameter value, where
       transport is the master.cf name of the message delivery transport.

       Note: transport_extra_recipient_limit parameters will not show up  in  "postconf"  command
       output  before Postfix version 2.9.  This limitation applies to many parameters whose name
       is a combination of a master.cf  service  name  and  a  built-in  suffix  (in  this  case:
       "_extra_recipient_limit").

transport_initial_destination_concurrency (default: $initial_destination_concurrency)

       A  transport-specific  override  for  the initial_destination_concurrency parameter value,
       where transport is the master.cf name of the message delivery transport.

       Note: some  transport_initial_destination_concurrency  parameters  will  not  show  up  in
       "postconf"  command  output  before  Postfix version 2.9.  This limitation applies to many
       parameters whose name is a combination of a master.cf service name and a  built-in  suffix
       (in this case: "_initial_destination_concurrency").

       This feature is available in Postfix 2.5 and later.

transport_maps (default: empty)

       Optional  lookup  tables  with  mappings  from  recipient  address  to  (message  delivery
       transport, next-hop destination).  See transport(5) for details.

       Specify zero or more "type:table" lookup tables, separated by whitespace or comma.  Tables
       will  be  searched in the specified order until a match is found.  If you use this feature
       with local files, run "postmap /etc/postfix/transport" after making a change.

       Pattern  matching  of  domain  names  is  controlled  by  the  presence  or   absence   of
       "transport_maps" in the parent_domain_matches_subdomains parameter value.

       For safety reasons, as of Postfix 2.3 this feature does not allow $number substitutions in
       regular expression maps.

       Examples:

       transport_maps = dbm:/etc/postfix/transport
       transport_maps = hash:/etc/postfix/transport

transport_minimum_delivery_slots (default: $default_minimum_delivery_slots)

       A transport-specific override  for  the  default_minimum_delivery_slots  parameter  value,
       where transport is the master.cf name of the message delivery transport.

       Note:  transport_minimum_delivery_slots  parameters will not show up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is  a  combination  of  a  master.cf  service  name  and  a built-in suffix (in this case:
       "_minimum_delivery_slots").

transport_recipient_limit (default: $default_recipient_limit)

       A transport-specific override  for  the  default_recipient_limit  parameter  value,  where
       transport is the master.cf name of the message delivery transport.

       Note:  some  transport_recipient_limit  parameters  will not show up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is  a  combination  of  a  master.cf  service  name  and  a built-in suffix (in this case:
       "_recipient_limit").

transport_recipient_refill_delay (default: $default_recipient_refill_delay)

       A transport-specific override  for  the  default_recipient_refill_delay  parameter  value,
       where transport is the master.cf name of the message delivery transport.

       Note:  transport_recipient_refill_delay  parameters will not show up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is  a  combination  of  a  master.cf  service  name  and  a built-in suffix (in this case:
       "_recipient_refill_delay").

       This feature is available in Postfix 2.4 and later.

transport_recipient_refill_limit (default: $default_recipient_refill_limit)

       A transport-specific override  for  the  default_recipient_refill_limit  parameter  value,
       where transport is the master.cf name of the message delivery transport.

       Note:  transport_recipient_refill_limit  parameters will not show up in "postconf" command
       output before Postfix version 2.9.  This limitation applies to many parameters whose  name
       is  a  combination  of  a  master.cf  service  name  and  a built-in suffix (in this case:
       "_recipient_refill_limit").

       This feature is available in Postfix 2.4 and later.

transport_retry_time (default: 60s)

       The time between attempts by the Postfix queue manager to contact a malfunctioning message
       delivery transport.

       Time  units:  s  (seconds), m (minutes), h (hours), d (days), w (weeks).  The default time
       unit is s (seconds).

transport_time_limit (default: $command_time_limit)

       A transport-specific override for the command_time_limit parameter value, where  transport
       is the master.cf name of the message delivery transport.

       Note: transport_time_limit parameters will not show up in "postconf" command output before
       Postfix version 2.9.   This  limitation  applies  to  many  parameters  whose  name  is  a
       combination   of   a  master.cf  service  name  and  a  built-in  suffix  (in  this  case:
       "_time_limit").

transport_transport_rate_delay (default: $default_transport_rate_delay)

       A transport-specific override for the default_transport_rate_delay parameter value,  where
       the  initial transport in the parameter name is the master.cf name of the message delivery
       transport.

trigger_timeout (default: 10s)

       The time limit for sending a trigger to a Postfix daemon (for example,  the  pickup(8)  or
       qmgr(8) daemon). This time limit prevents programs from getting stuck when the mail system
       is under heavy load.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).   The  default  time
       unit is s (seconds).

undisclosed_recipients_header (default: see postconf -d output)

       Message  header  that the Postfix cleanup(8) server inserts when a message contains no To:
       or Cc: message header. With Postfix 2.8 and  later,  the  default  value  is  empty.  With
       Postfix 2.4-2.7, specify an empty value to disable this feature.

       Example:

       # Default value before Postfix 2.8.
       # Note: the ":" and ";" are both required.
       undisclosed_recipients_header = To: undisclosed-recipients:;

unknown_address_reject_code (default: 450)

       The  numerical  response  code  when the Postfix SMTP server rejects a sender or recipient
       address because its domain is unknown.  This is one  of  the  possible  replies  from  the
       restrictions reject_unknown_sender_domain and reject_unknown_recipient_domain.

       Do not change this unless you have a complete understanding of RFC 5321.

unknown_address_tempfail_action (default: $reject_tempfail_action)

       The    Postfix    SMTP    server's    action    when    reject_unknown_sender_domain    or
       reject_unknown_recipient_domain fail due to a temporary error condition.  Specify  "defer"
       to  defer  the  remote SMTP client request immediately. With the default "defer_if_permit"
       action, the Postfix SMTP server continues to look for opportunities to  reject  mail,  and
       defers the client request only if it would otherwise be accepted.

       This feature is available in Postfix 2.6 and later.

unknown_client_reject_code (default: 450)

       The  numerical  Postfix  SMTP server response code when a client without valid address <=>
       name mapping is rejected  by  the  reject_unknown_client_hostname  restriction.  The  SMTP
       server always replies with 450 when the mapping failed due to a temporary error condition.

       Do not change this unless you have a complete understanding of RFC 5321.

unknown_helo_hostname_tempfail_action (default: $reject_tempfail_action)

       The  Postfix  SMTP  server's  action  when  reject_unknown_helo_hostname  fails  due to an
       temporary error condition. Specify  "defer"  to  defer  the  remote  SMTP  client  request
       immediately.  With the default "defer_if_permit" action, the Postfix SMTP server continues
       to look for opportunities to reject mail, and defers the client request only if  it  would
       otherwise be accepted.

       This feature is available in Postfix 2.6 and later.

unknown_hostname_reject_code (default: 450)

       The  numerical Postfix SMTP server response code when the hostname specified with the HELO
       or EHLO command is rejected by the reject_unknown_helo_hostname restriction.

       Do not change this unless you have a complete understanding of RFC 5321.

unknown_local_recipient_reject_code (default: 550)

       The numerical Postfix SMTP server response code when a recipient  address  is  local,  and
       $local_recipient_maps specifies a list of lookup tables that does not match the recipient.
       A recipient address is local when its domain matches $mydestination, $proxy_interfaces  or
       $inet_interfaces.

       The  default  setting is 550 (reject mail) but it is safer to initially use 450 (try again
       later) so you have time to find out if your local_recipient_maps settings are OK.

       Example:

       unknown_local_recipient_reject_code = 450

       This feature is available in Postfix 2.0 and later.

unknown_relay_recipient_reject_code (default: 550)

       The  numerical  Postfix  SMTP  server  reply  code  when  a  recipient   address   matches
       $relay_domains,  and  relay_recipient_maps specifies a list of lookup tables that does not
       match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_alias_reject_code (default: 550)

       The   Postfix   SMTP   server   reply   code   when   a    recipient    address    matches
       $virtual_alias_domains,  and  $virtual_alias_maps  specifies  a list of lookup tables that
       does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_mailbox_reject_code (default: 550)

       The   Postfix   SMTP   server   reply   code   when   a    recipient    address    matches
       $virtual_mailbox_domains, and $virtual_mailbox_maps specifies a list of lookup tables that
       does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unverified_recipient_defer_code (default: 450)

       The numerical Postfix SMTP server response when a recipient address probe fails due  to  a
       temporary error condition.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the address anyway.

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.6 and later.

unverified_recipient_reject_code (default: 450)

       The  numerical  Postfix  SMTP  server response when a recipient address is rejected by the
       reject_unverified_recipient restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the address anyway.

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.1 and later.

unverified_recipient_reject_reason (default: empty)

       The Postfix SMTP server's reply when rejecting mail with  reject_unverified_recipient.  Do
       not  include  the  numeric  SMTP  reply  code or the enhanced status code. By default, the
       response includes actual address verification details.

       Example:

       unverified_recipient_reject_reason = Recipient address lookup failed

       This feature is available in Postfix 2.6 and later.

unverified_recipient_tempfail_action (default: $reject_tempfail_action)

       The Postfix SMTP server's action when reject_unverified_recipient fails due to a temporary
       error condition. Specify "defer" to defer the remote SMTP client request immediately. With
       the default "defer_if_permit" action, the  Postfix  SMTP  server  continues  to  look  for
       opportunities  to reject mail, and defers the client request only if it would otherwise be
       accepted.

       This feature is available in Postfix 2.6 and later.

unverified_sender_defer_code (default: 450)

       The numerical Postfix SMTP server response code when a sender address probe fails due to a
       temporary error condition.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the address anyway.

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.6 and later.

unverified_sender_reject_code (default: 450)

       The  numerical  Postfix  SMTP server response code when a recipient address is rejected by
       the reject_unverified_sender restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the address anyway.

       Do not change this unless you have a complete understanding of RFC 5321.

       This feature is available in Postfix 2.1 and later.

unverified_sender_reject_reason (default: empty)

       The Postfix SMTP server's reply when rejecting mail with reject_unverified_sender. Do  not
       include  the numeric SMTP reply code or the enhanced status code. By default, the response
       includes actual address verification details.

       Example:

       unverified_sender_reject_reason = Sender address lookup failed

       This feature is available in Postfix 2.6 and later.

unverified_sender_tempfail_action (default: $reject_tempfail_action)

       The Postfix SMTP server's action when reject_unverified_sender fails due  to  a  temporary
       error condition. Specify "defer" to defer the remote SMTP client request immediately. With
       the default "defer_if_permit" action, the  Postfix  SMTP  server  continues  to  look  for
       opportunities  to reject mail, and defers the client request only if it would otherwise be
       accepted.

       This feature is available in Postfix 2.6 and later.

verp_delimiter_filter (default: -=+)

       The characters Postfix accepts as VERP delimiter characters  on  the  Postfix  sendmail(1)
       command line and in SMTP commands.

       This feature is available in Postfix 1.1 and later.

virtual_alias_address_length_limit (default: 1000)

       The  maximal length of an email address after virtual alias expansion.  This stops virtual
       aliasing loops that increase the address length exponentially.

       This feature is available in Postfix 3.0 and later.

virtual_alias_domains (default: $virtual_alias_maps)

       Postfix is final destination for the specified list of virtual  alias  domains,  that  is,
       domains for which all addresses are aliased to addresses in other local or remote domains.
       The SMTP  server  validates  recipient  addresses  with  $virtual_alias_maps  and  rejects
       non-existent   recipients.   See   also   the   virtual   alias   domain   class   in  the
       ADDRESS_CLASS_README file

       This feature is available in Postfix  2.0  and  later.  The  default  value  is  backwards
       compatible with Postfix version 1.1.

       The  default  value  is  $virtual_alias_maps  so  that  you can keep all information about
       virtual alias domains in one place.  If you have many users,  it  is  better  to  separate
       information  that  changes  more  frequently  (virtual  address -> local or remote address
       mapping) from information that changes less frequently (the list of virtual domain names).

       Specify a list of host or domain names, "/file/name" or "type:table"  patterns,  separated
       by  commas  and/or  whitespace.  A  "/file/name"  pattern  is  replaced by its contents; a
       "type:table" lookup table is matched when a table  entry  matches  a  lookup  string  (the
       lookup result is ignored).  Continue long lines by starting the next line with whitespace.
       Specify "!pattern" to exclude a host or domain name from the list. The form  "!/file/name"
       is supported only in Postfix version 2.4 and later.

       See also the VIRTUAL_README and ADDRESS_CLASS_README documents for further information.

       Example:

       virtual_alias_domains = virtual1.tld virtual2.tld

virtual_alias_expansion_limit (default: 1000)

       The  maximal  number of addresses that virtual alias expansion produces from each original
       recipient.

       This feature is available in Postfix 2.1 and later.

virtual_alias_maps (default: $virtual_maps)

       Optional lookup tables that alias specific mail addresses or domains  to  other  local  or
       remote  address.   The  table  format  and  lookups  are  documented in virtual(5). For an
       overview of Postfix address manipulations see the ADDRESS_REWRITING_README document.

       This feature is available in Postfix  2.0  and  later.  The  default  value  is  backwards
       compatible with Postfix version 1.1.

       Specify  zero  or more "type:name" lookup tables, separated by whitespace or comma. Tables
       will be searched in the specified order until a match is found.  Note: these  lookups  are
       recursive.

       If  you  use  this  feature  with  indexed files, run "postmap /etc/postfix/virtual" after
       changing the file.

       Examples:

       virtual_alias_maps = dbm:/etc/postfix/virtual
       virtual_alias_maps = hash:/etc/postfix/virtual

virtual_alias_recursion_limit (default: 1000)

       The maximal nesting depth of virtual alias expansion.  Currently the  recursion  limit  is
       applied  only  to  the left branch of the expansion graph, so the depth of the tree can in
       the worst case reach the sum of the expansion and recursion limits.  This  may  change  in
       the future.

       This feature is available in Postfix 2.1 and later.

virtual_delivery_status_filter (default: $default_delivery_status_filter)

       Optional  filter  for  the virtual(8) delivery agent to change the delivery status code or
       explanatory    text     of     successful     or     unsuccessful     deliveries.      See
       default_delivery_status_filter for details.

       This feature is available in Postfix 3.0 and later.

virtual_destination_concurrency_limit (default: $default_destination_concurrency_limit)

       The  maximal number of parallel deliveries to the same destination via the virtual message
       delivery transport. This limit is enforced by the  queue  manager.  The  message  delivery
       transport name is the first field in the entry in the master.cf file.

virtual_destination_recipient_limit (default: $default_destination_recipient_limit)

       The  maximal  number of recipients per message for the virtual message delivery transport.
       This limit is enforced by the queue manager. The message delivery transport  name  is  the
       first field in the entry in the master.cf file.

       Setting    this    parameter    to    a    value    of    1   changes   the   meaning   of
       virtual_destination_concurrency_limit from concurrency per  domain  into  concurrency  per
       recipient.

virtual_gid_maps (default: empty)

       Lookup tables with the per-recipient group ID for virtual(8) mailbox delivery.

       This  parameter is specific to the virtual(8) delivery agent.  It does not apply when mail
       is delivered with a different mail delivery program.

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.  Tables
       will be searched in the specified order until a match is found.

       In  a  lookup  table,  specify  a left-hand side of "@domain.tld" to match any user in the
       specified domain that does not have a specific "user@domain.tld" entry.

       When a recipient address has an  optional  address  extension  (user+foo@domain.tld),  the
       virtual(8)  delivery  agent looks up the full address first, and when the lookup fails, it
       looks up the unextended address (user@domain.tld).

       Note 1: for security reasons, the virtual(8) delivery agent disallows  regular  expression
       substitution  of  $1  etc.  in regular expression lookup tables, because that would open a
       security hole.

       Note 2: for security reasons, the virtual(8) delivery agent will silently ignore  requests
       to  use  the  proxymap(8)  server. Instead it will open the table directly. Before Postfix
       version 2.2, the virtual(8) delivery agent will terminate with a fatal error.

virtual_mailbox_base (default: empty)

       A prefix that the  virtual(8)  delivery  agent  prepends  to  all  pathname  results  from
       $virtual_mailbox_maps  table  lookups.   This is a safety measure to ensure that an out of
       control map doesn't litter the file system  with  mailboxes.   While  virtual_mailbox_base
       could be set to "/", this setting isn't recommended.

       This  parameter is specific to the virtual(8) delivery agent.  It does not apply when mail
       is delivered with a different mail delivery program.

       Example:

       virtual_mailbox_base = /var/mail

virtual_mailbox_domains (default: $virtual_mailbox_maps)

       Postfix is final destination for the specified list of domains; mail is delivered via  the
       $virtual_transport  mail  delivery  transport.   By default this is the Postfix virtual(8)
       delivery agent.  The SMTP server validates recipient addresses with  $virtual_mailbox_maps
       and  rejects  mail for non-existent recipients.  See also the virtual mailbox domain class
       in the ADDRESS_CLASS_README file.

       This parameter expects the same syntax as the mydestination configuration parameter.

       This feature is available in Postfix  2.0  and  later.  The  default  value  is  backwards
       compatible with Postfix version 1.1.

virtual_mailbox_limit (default: 51200000)

       The maximal size in bytes of an individual virtual(8) mailbox or maildir file, or zero (no
       limit).

       This parameter is specific to the virtual(8) delivery agent.  It does not apply when  mail
       is delivered with a different mail delivery program.

virtual_mailbox_lock (default: see postconf -d output)

       How  to  lock  a  UNIX-style virtual(8) mailbox before attempting delivery.  For a list of
       available file locking methods, use the "postconf -l" command.

       This parameter is specific to the virtual(8) delivery agent.  It does not apply when  mail
       is delivered with a different mail delivery program.

       This  setting  is  ignored  with  maildir style delivery, because such deliveries are safe
       without application-level locks.

       Note 1: the dotlock method requires that the recipient UID or GID has write access to  the
       parent directory of the recipient's mailbox file.

       Note 2: the default setting of this parameter is system dependent.

virtual_mailbox_maps (default: empty)

       Optional   lookup   tables   with   all   valid   addresses  in  the  domains  that  match
       $virtual_mailbox_domains.

       Specify zero or more "type:name" lookup tables, separated by whitespace or  comma.  Tables
       will be searched in the specified order until a match is found.

       In  a  lookup  table,  specify  a left-hand side of "@domain.tld" to match any user in the
       specified domain that does not have a specific "user@domain.tld" entry.

       The remainder of this text is specific to the virtual(8)  delivery  agent.   It  does  not
       apply when mail is delivered with a different mail delivery program.

       The  virtual(8)  delivery  agent  uses  this table to look up the per-recipient mailbox or
       maildir pathname.  If the lookup result ends in a slash ("/"), maildir-style  delivery  is
       carried  out,  otherwise  the  path is assumed to specify a UNIX-style mailbox file.  Note
       that $virtual_mailbox_base is unconditionally prepended to this path.

       When a recipient address has an  optional  address  extension  (user+foo@domain.tld),  the
       virtual(8)  delivery  agent looks up the full address first, and when the lookup fails, it
       looks up the unextended address (user@domain.tld).

       Note 1: for security reasons, the virtual(8) delivery agent disallows  regular  expression
       substitution  of  $1  etc.  in regular expression lookup tables, because that would open a
       security hole.

       Note 2: for security reasons, the virtual(8) delivery agent will silently ignore  requests
       to  use  the  proxymap(8)  server. Instead it will open the table directly. Before Postfix
       version 2.2, the virtual(8) delivery agent will terminate with a fatal error.

virtual_maps (default: empty)

       Optional lookup tables with a) names of domains for which all  addresses  are  aliased  to
       addresses in other local or remote domains, and b) addresses that are aliased to addresses
       in other local or remote domains.  Available before  Postfix  version  2.0.  With  Postfix
       version  2.0  and  later, this is replaced by separate controls: virtual_alias_domains and
       virtual_alias_maps.

virtual_minimum_uid (default: 100)

       The minimum user ID value that the virtual(8) delivery agent  accepts  as  a  result  from
       $virtual_uid_maps  table lookup.  Returned values less than this will be rejected, and the
       message will be deferred.

       This parameter is specific to the virtual(8) delivery agent.  It does not apply when  mail
       is delivered with a different mail delivery program.

virtual_transport (default: virtual)

       The default mail delivery transport and next-hop destination for final delivery to domains
       listed  with  $virtual_mailbox_domains.   This  information  can  be  overruled  with  the
       transport(5) table.

       Specify  a  string  of  the  form transport:nexthop, where transport is the name of a mail
       delivery transport defined in master.cf.  The :nexthop destination is optional; its syntax
       is documented in the manual page of the corresponding delivery agent.

       This feature is available in Postfix 2.0 and later.

virtual_uid_maps (default: empty)

       Lookup tables with the per-recipient user ID that the virtual(8) delivery agent uses while
       writing to the recipient's mailbox.

       This parameter is specific to the virtual(8) delivery agent.  It does not apply when  mail
       is delivered with a different mail delivery program.

       Specify  zero  or more "type:name" lookup tables, separated by whitespace or comma. Tables
       will be searched in the specified order until a match is found.

       In a lookup table, specify a left-hand side of "@domain.tld" to  match  any  user  in  the
       specified domain that does not have a specific "user@domain.tld" entry.

       When  a  recipient  address  has  an optional address extension (user+foo@domain.tld), the
       virtual(8) delivery agent looks up the full address first, and when the lookup  fails,  it
       looks up the unextended address (user@domain.tld).

       Note  1:  for security reasons, the virtual(8) delivery agent disallows regular expression
       substitution of $1 etc. in regular expression lookup tables, because  that  would  open  a
       security hole.

       Note  2: for security reasons, the virtual(8) delivery agent will silently ignore requests
       to use the proxymap(8) server. Instead it will open the  table  directly.  Before  Postfix
       version 2.2, the virtual(8) delivery agent will terminate with a fatal error.

SEE ALSO

       postconf(1), Postfix configuration parameter maintenance
       master(5), Postfix daemon configuration maintenance

LICENSE

       The Secure Mailer license must be distributed with this software.

AUTHOR(S)

       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA

       Viktor Dukhovni

                                                                                      POSTCONF(5)