Provided by: postfix_2.11.0-1_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 "$name", "${name}" or "$(name)" are recursively replaced  by
                     the value of the named parameter.

              ·      The expression "${name?value}" expands to "value" when "$name" is non-empty.
                     This form is supported with Postfix version 2.2 and later.

              ·      The expression "${name:value}" expands to "value"  when  "$name"  is  empty.
                     This form is supported with Postfix version 2.2 and later.

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

       ·      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_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.

       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, or via the MAIL_CONFIG environment parameter.

       This list must be specified in the default Postfix configuration directory, and is used by
       set-gid Postfix commands such as postqueue(1) and postdrop(1).

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.

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: 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  inter-operability  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.

       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.

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.

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  parent_domain_matches_subdomains
       parameter.

       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_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_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 small delay values 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.

       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.

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

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_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 X-Original-To message header. This  header  is  needed  for  multi-
       recipient mailboxes.

       When this parameter is set to yes, the cleanup(8) daemon performs duplicate elimination on
       distinct pairs of (original  recipient,  rewritten  recipient),  and  generates  non-empty
       original recipient queue file records.

       When  this parameter is set to no, the cleanup(8) daemon performs duplicate elimination on
       the rewritten recipient address only, and generates empty original  recipient  queue  file
       records.

       This  feature is available in Postfix 2.1 and later. With Postfix version 2.0, support for
       the X-Original-To message header is always turned on. Postfix versions before 2.0 have  no
       support for the X-Original-To message header.

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. The
       name=value form is supported with Postfix version 2.1 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.

       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_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 Postfix process will import from  a  non-Postfix
       parent process. Examples of relevant parameters:

       TZ     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. The
       name=value form is supported with Postfix version 2.1 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_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_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_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_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_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.

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: export)

       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: empty)

       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)

       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: empty)

       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_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.

       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.

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.

       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_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.

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_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: 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: 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.  Don't do this with a
              dialup site - it would 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

owner_request_special (default: yes)

       Give  special  treatment  to owner-listname and listname-request address localparts: don't
       split such addresses when the recipient_delimiter is set to "-".  This feature  is  useful
       for mailing lists.

parent_domain_matches_subdomains (default: see postconf -d output)

       What Postfix features match subdomains of "domain.tld" automatically, instead of requiring
       an explicit ".domain.tld" pattern.  This is planned backwards compatibility:   eventually,
       all  Postfix  features  are expected to require explicit ".domain.tld" style patterns when
       you really want to match subdomains.

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.

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.

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.

        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: ${stress?10}${stress:300}s)

       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_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_ttl (default: 1h)

       The  amount of time that postscreen(8) will use the result from a successful DNS blocklist
       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_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: ${stress?2}${stress:6}s)

       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.  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.

       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.

       This feature is available in Postfix 2.1 and later.

       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.

       Specify  the  types  and  names  of  databases  to  use.   After  change,   run   "postmap
       /etc/postfix/recipient_bcc".

       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:

       recipient_bcc_maps = hash:/etc/postfix/recipient_bcc

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_delimiters = +-

       # 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: $mydestination)

       What destination domains  (and  subdomains  thereof)  this  system  will  relay  mail  to.
       Subdomain  matching is controlled with the parent_domain_matches_subdomains parameter. 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.

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.

       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).

       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,
       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.  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 inter-
       operability 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.

       This feature is available in Postfix 2.1 and later.

       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.

       Specify  the  types  and  names  of  databases  to  use.   After  change,   run   "postmap
       /etc/postfix/sender_bcc".

       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

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.

       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.

       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_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".

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.  With Postfix  2.8
       the default is "ipv6".

       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_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_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_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.

       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_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.

       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 EHLO or HELO 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.

       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 inter-operability 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  remote
       hostname or domain, or sender address 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.

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_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 certificate 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 certificate 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 certificate 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  inter-operability
       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: export)

       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 "export" ensures maximum inter-
       operability.  Because  encryption  is optional, stronger controls are not appropriate, and
       this setting SHOULD NOT be changed unless the change is essential.

       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.

       Example:
       smtp_tls_ciphers = export

       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_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,
       certificate  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  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, disable logging of TLS
              activity.

              1 Also log remote SMTP server trust-chain verification errors and peer  certificate
              summary   information.  With  Postfix  2.8  and  earlier,  log  TLS  handshake  and
              certificate information.

              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.   This  is  the  default for
              opportunistic encryption. It is not recommended for mandatory encryption unless you
              must  enforce TLS with "crippled" peers. The underlying cipherlist is specified via
              the  tls_export_cipherlist  configuration  parameter,  which   you   are   strongly
              encouraged to not change.

       low    Enable "LOW" grade or better OpenSSL ciphers.  This setting is only appropriate for
              internal  mail  servers.   The  underlying  cipherlist   is   specified   via   the
              tls_low_cipherlist  configuration  parameter,  which you are strongly encouraged to
              not change.

       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)

       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".

       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".

       Since  SSL  version  2  has  known  protocol weaknesses and is now deprecated, the default
       setting excludes "SSLv2".  This means that by default, SSL version 2 will not be  used  at
       the "encrypt" security level and higher.

       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.

       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 inter-operability. 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 6698 (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 6698 (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 certificate 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)

       List  of  TLS  protocols  that  the  Postfix  SMTP  client  will  exclude  or include with
       opportunistic TLS encryption. Starting with Postfix 2.6, the Postfix SMTP client  will  by
       default not use the obsolete SSLv2 protocol.

       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 even 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  inter-operability.   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 6698) 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 6698 (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 6698 (DANE) TLS authentication is available with Postfix
              2.11 and later.

       fingerprint
              Certificate fingerprint verification.  At this security level, there are no trusted
              certificate  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

       # 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 6698 (DANE TLSA), which defines mechanisms
       for a client 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_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_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.

       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_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_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  EHLO  or  HELO  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 inter-operability 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:]]+)'>(.*)/     RCPT TO:<$1>$2

           # 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:<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+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 table is not searched by hostname for robustness reasons.

       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_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_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  unknown_hostname_reject_code  parameter  specifies the numerical response code
              for rejected requests (default: 450).
              The unknown_helo_hostname_tempfail_action parameter specifies the  action  after  a
              temporary  DNS error (default: defer_if_permit). 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_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_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_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_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_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 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 A or MX record or 2) a malformed MX record
              such as a record with a zero-length MX hostname (Postfix version 2.3 and later).
              The unknown_address_reject_code parameter specifies the numerical response code for
              rejected  requests  (default:  450).   The  response  is  always  450  in case of a
              temporary DNS error.
              The  unknown_address_tempfail_action  parameter  specifies  the  action   after   a
              temporary DNS error (default: defer_if_permit).

       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 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 sender (MAIL FROM) addresses.

       Specify  zero  or more "type:table" lookup tables. 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_mx_access type:table
              Search the specified access(5) database for the MX hosts for the MAIL FROM address,
              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
              address,  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  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 A or MX record, or 2) a malformed MX record
              such as a record with a zero-length MX hostname (Postfix version 2.3 and later).
              The unknown_address_reject_code parameter specifies the numerical response code for
              rejected  requests  (default:  450).   The  response  is  always  450  in case of a
              temporary DNS error.
              The  unknown_address_tempfail_action  parameter  specifies  the  action   after   a
              temporary DNS error (default: defer_if_permit).

       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 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 certificate 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 certificate 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  certificate  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 certificate 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 certificate
       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
       certificate 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 inter-operability 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: export)

       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 "export" ensures maximum inter-
       operability. Because encryption is optional, stronger controls are  not  appropriate,  and
       this setting SHOULD NOT be changed unless the change is essential.

       When  TLS  is  mandatory  the  cipher  grade is chosen via the smtpd_tls_mandatory_ciphers
       configuration parameter, see there for syntax details.

       Example:
       smtpd_tls_ciphers = export

       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.

       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.

       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 Log only a summary message on TLS handshake completion -  no  logging  of  remote
              SMTP  client  certificate  trust-chain  verification  errors  if client certificate
              verification is not required. With Postfix 2.8 and earlier, disable logging of  TLS
              activity.

              1  Also  log  trust-chain verification errors and peer certificate name and issuer.
              With Postfix 2.8 and earlier, log TLS handshake and certificate information.

              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.  This is the most appropriate
              setting for public MX hosts, and is always used with opportunistic TLS  encryption.
              The  underlying cipherlist is specified via the tls_export_cipherlist configuration
              parameter, which you are strongly encouraged to not change.

       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.

       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)

       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.

       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".

       Since  SSL  version  2  has  known  protocol weaknesses and is now deprecated, the default
       setting excludes "SSLv2".  This means that by default, SSL version 2 will not be  used  at
       the "encrypt" security level.

       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: empty)

       List  of  TLS  protocols  that  the  Postfix  SMTP  server  will  exclude  or include with
       opportunistic TLS encryption. This parameter SHOULD be left at its  default  empty  value,
       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 even 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

       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.

       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.

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.

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)

       The  mail  system  name  that  is prepended to the process name in syslog records, so that
       "smtpd" becomes, for example, "postfix/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  certificate  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 DANE TLSA digest algorithm agility.  When digest algorithm agility  is  enabled,
       and  the  server  and  client  support a common strong digest algorithm, TLSA records with
       weaker digest algorithms are ignored.

       Specify one of the following:

       off    DANE verification examines each well-formed record in the TLSA RRset whose matching
              type  is  either  "0"  (no  hash used) or is one of the digest algorithms listed in
              $tls_dane_digests.  This setting is not recommended.

       on     From each group of well-formed TLSA RRs a non-zero digest matching  type  with  the
              same  certificate usage and selector, DANE verification examines only those records
              whose  matching   type   has   the   highest   precedence   (appear   earliest   in
              $tls_dane_digests).

       maybe  For  compatibility  with  digest  algorithm agility, each certificate or public key
              whose digest is included in a DANE TLSA RRset, SHOULD be published  with  the  same
              set  of  digest matching type values as any other with the same usage and selector.
              Therefore, compatible TLSA RRsets will contain an identical  count  of  well-formed
              RRs  with each non-zero digest matching type for any fixed combination of usage and
              selector.  When this constraint is violated, or  any  of  the  digest  records  are
              malformed,  digest  algorithm  agility  will disabled.  Otherwise, digest algorithm
              agility is enabled.

       Digest algorithm agility ensures that the strongest digest supported by both  the  Postfix
       SMTP  client and the remote server is used, and weaker digests are ignored.  This supports
       non-disruptive deprecation of outdated digest algorithms.

       To ensure compatibility  with  digest  algorithm  agility  during  key  rotation,  when  a
       certificate  or  public  key is being replaced with another, and both are published during
       the transition, both the old and the new certificate MUST be specified with the  same  set
       of  digests.   One  can  change  the  list  of  digest algorithms later, once old keys are
       retired.  At any given time, change either the list of digests without changing  the  list
       of certificates or public keys or the list of certificates or public keys without changing
       the list of digests.  Full value matching  type  "0"  records  are  not  subject  to  this
       constraint, but are discouraged due to the size of the resulting DNS records.

       It  is  expected  that  this  algorithm agility mechanism will be published in a standards
       track RFC for SMTP with DANE, and also in an eventual update to RFC 6698.

       This feature is available in Postfix 2.11 and later.

tls_dane_digests (default: sha512 sha256)

       RFC 6698 TLSA 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.

       When for a particular combination of "certificate usage" and  "selector"  the  TLSA  RRset
       contains  records  with  more  than  one digest matching type, the tls_dane_digest_agility
       parameter determines whether all the RRs are used, or only those with the  most  preferred
       digest matching type.

       The tls_dane_trust_anchor_digest_enable parameter controls whether any digest TLSA records
       are acceptable in usage "2" (trust anchor assertion) TLSA records.

       This feature is available in Postfix 2.11 and later.

tls_dane_trust_anchor_digest_enable (default: yes)

       RFC 6698 trust-anchor digest support in the Postfix TLS library.  Enable support  for  RFC
       6698  (DANE TLSA) DNS records that contain digests of trust-anchors with certificate usage
       "2".  In this case the certificate usage logically requires the  server  administrator  to
       configure  the  server  to  include  the  trust-anchor  certificate  in  the  server's SSL
       certificate chain.  If enough domains mess this up, you can disable support for these TLSA
       records,  but  you'll no longer have secure connections that get it right and only publish
       trust anchor records.

       At the dane security level, when a TLSA RRset includes  only  unusable  associations,  the
       Postfix  SMTP  client  will  automatically  switch  the connection to the encrypt security
       level.  At the dane-only security level, the server in question is skipped and delivery is
       deferred if no secure servers are found.

       The  tls_dane_digests  parameter controls the list of digest algorithms that are supported
       in  TLSA  records.   The  tls_dane_digest_agility  parameter  controls  digest   algorithm
       downgrade attack resistance.

       This feature is available in Postfix 2.11 and later.

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_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 "exotic" 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: ALL:+RC4:@STRENGTH)

       The OpenSSL cipherlist for "EXPORT" or higher grade ciphers. This defines the  meaning  of
       the   "export"  setting  in  smtpd_tls_mandatory_ciphers,  smtp_tls_mandatory_ciphers  and
       lmtp_tls_mandatory_ciphers. This is the  cipherlist  for  the  opportunistic  ("may")  TLS
       client  security level and is the default cipherlist for the SMTP server. You are strongly
       encouraged to not change this setting. With OpenSSL 1.0.0 and  later  the  cipherlist  may
       start  with  an "aNULL:" prefix, which restores the 0.9.8-compatible ordering of the aNULL
       ciphers to the top of the list when they are enabled.  This  prefix  is  not  needed  with
       previous OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_high_cipherlist (default: ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)

       The  OpenSSL  cipherlist  for "HIGH" grade ciphers. This defines the meaning of the "high"
       setting      in      smtpd_tls_mandatory_ciphers,      smtp_tls_mandatory_ciphers      and
       lmtp_tls_mandatory_ciphers.  You  are strongly encouraged to not change this setting. With
       OpenSSL 1.0.0 and later the cipherlist may start with an "aNULL:" prefix,  which  restores
       the  0.9.8-compatible  ordering  of the aNULL ciphers to the top of the list when they are
       enabled. This prefix is not needed with previous OpenSSL releases.

       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: ALL:!EXPORT:+RC4:@STRENGTH)

       The  OpenSSL cipherlist for "LOW" or higher grade ciphers. This defines the meaning of the
       "low"   setting    in    smtpd_tls_mandatory_ciphers,    smtp_tls_mandatory_ciphers    and
       lmtp_tls_mandatory_ciphers.  You are strongly encouraged to not change this setting.  With
       OpenSSL 1.0.0 and later the cipherlist may start with an "aNULL:" prefix,  which  restores
       the  0.9.8-compatible  ordering  of the aNULL ciphers to the top of the list when they are
       enabled. This prefix is not needed with previous OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_medium_cipherlist (default: ALL:!EXPORT:!LOW:+RC4:@STRENGTH)

       The OpenSSL cipherlist for "MEDIUM" or higher grade ciphers. This defines the  meaning  of
       the   "medium"  setting  in  smtpd_tls_mandatory_ciphers,  smtp_tls_mandatory_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). You
       are strongly encouraged to not change this setting.  With  OpenSSL  1.0.0  and  later  the
       cipherlist may start with an "aNULL:" prefix, which restores the 0.9.8-compatible ordering
       of the aNULL ciphers to the top of the list when they are  enabled.  This  prefix  is  not
       needed with previous OpenSSL releases.

       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_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.

       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.  If you use this feature with local
       files, run "postmap /etc/postfix/transport" after making a change.

       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").

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 Postfix SMTP server response code when a  sender  or  recipient  address  is
       rejected    by   the   reject_unknown_sender_domain   or   reject_unknown_recipient_domain
       restriction.  The response is always 450 in case of a temporary DNS error.

       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_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.

       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_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.

       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.

       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.

       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

                                                                                      POSTCONF(5)