Provided by: postfix_2.7.0-1_i386 bug

NAME

       postconf - Postfix configuration parameters

SYNOPSIS

       postconf parameter ...

       postconf -e "parameter=value" ...

DESCRIPTION

       The  Postfix main.cf configuration file specifies a small subset of all
       the parameters that control the operation of the Postfix  mail  system.
       Parameters not specified in main.cf 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
       2821.

       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
       2821.

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: ${stress?1}${stress:3})

       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 2.6 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_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: 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:

       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: if mail to the BCC address bounces it will  be  returned  to  the
       sender.

       Note:  automatic  BCC  recipients  are  produced only for new mail.  To
       avoid mailer loops, automatic BCC recipients are not generated for mail
       that  Postfix  forwards internally, nor for mail that Postfix generates
       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
       server’s 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  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)

       The maximal time a bounce message is queued  before  it  is  considered
       undeliverable.  By default, this is the same as the queue life time 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 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 system-wide recipient address extension delimiter.

       ${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_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.

       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;  with per-destination recipient
       limit > 1, a destination is a domain, otherwise it is a recipient.

       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.

       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 changes the meaning of the
       corresponding per-destination concurrency limit  from  concurrency  per
       domain into concurrency per 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  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
       2821.

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.

       This feature is enabled with the delay_warning_time parameter.

delay_warning_time (default: 0h)

       The time after which the sender receives 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).

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.

       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

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_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 system-wide recipient address extension delimiter.

       ${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.

       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 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 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: ipv4)

       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.

       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 to DNS type A record lookups, 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 attempt to connect via IPv6 before attempting to use IPv4.

       Examples:

       inet_protocols = ipv4 (DEFAULT)
       inet_protocols = all
       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
       2821.

ipc_idle (default: version dependent)

       The time after which a client closes  an  idle  internal  communication
       channel.   The  purpose  is  to  allow servers to terminate voluntarily
       after they become idle. This is  used,  for  example,  by  the  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 servers to terminate voluntarily
       after reaching their client limit.  This is used, for example,  by  the
       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.

lmtp_assume_final (default: no)

       When  an  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 infinetisimal 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 LMTP servers in use, and the concurrency limit specified  for
       the  LMTP  client.  Cached  connections  are  closed  under  any of the
       following conditions:

       ·      The 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  LMTP  server
              associated with the current session does not respond to the RSET
              command.

       Most of these limitations will be removed after  Postfix  implements  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 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_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 LMTP client time limit for sending the LMTP ".", and for  receiving
       the 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  LMTP  client time limit for sending the LMTP DATA command, and for
       receiving the 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  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  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  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_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  LMTP  client  time  limit  for  sending  the LHLO command, and for
       receiving the initial 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 LMTP client time limit for sending the MAIL FROM command,  and  for
       receiving the 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_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 LMTP client time limit  for  sending  the  QUIT  command,  and  for
       receiving the 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 LMTP client time limit for sending the RCPT  TO  command,  and  for
       receiving the 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  LMTP  client  time  limit  for  sending  the RSET command, and for
       receiving the 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 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_xforward_command (default: no)

       Send  an  XFORWARD command to the 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 0.9.9 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 0.9.9 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_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: SSLv3, TLSv1)

       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_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  LMTP  client  time limit for sending the XFORWARD command, and for
       receiving the 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 /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_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 client
              TLS  certificate  fingerprint  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 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 system-wide recipient address extension delimiter.

       $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 a user  account  that  does  not
       share  a  group  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_sender   or   reject_rhsbl_recipient
       restriction.

       Do  not  change  this  unless  you have a complete understanding of RFC
       2821.

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:

       # 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)

       The  maximal  time  a  message  is  queued  before  it  is sent back as
       undeliverable.

       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 \\.

       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 \\.

       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
       2821.

       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.  $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
       name  from  gethostname(),  which  is  expected to be a fully-qualified
       domain name.  If it is only one component, then $mydomain  is  appended
       to  it.  $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" SMTP  clients  that  have  more  privileges  than
       "strangers".

       In particular, "trusted" SMTP clients are allowed to relay mail through
       Postfix.  See the smtpd_recipient_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"
              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"
              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".  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).

       delay  Send the postmaster copies of the headers of delayed  mail.  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.

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_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_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 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 clients are allowed to connect to the 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 QMQP server will pause before sending a negative reply to
       the 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 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  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:  if  mail  to  the BCC address bounces it will be returned to the
       sender.

       Note: automatic BCC recipients are produced  only  for  new  mail.   To
       avoid mailer loops, automatic BCC recipients are not generated for mail
       that Postfix forwards internally, nor for mail that  Postfix  generates
       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  separator  between  user  names and address extensions (user+foo).
       See canonical(5), local(8), relocated(5) and virtual(5) for the effects
       this has on aliases, canonical, virtual, relocated and on .forward file
       lookups.  Basically,  the  software  tries  user+foo  and  .forward+foo
       before trying user and .forward.

       Example:

       recipient_delimiter = +

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
       2821.

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  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.

       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
       2821.

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).

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:  if  mail  to  the BCC address bounces it will be returned to the
       sender.

       Note: automatic BCC recipients are produced  only  for  new  mail.   To
       avoid mailer loops, automatic BCC recipients are not generated for mail
       that Postfix forwards internally, nor for mail that  Postfix  generates
       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_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_always_send_ehlo (default: yes)

       Always send EHLO at the start of an SMTP session.

       With  "smtp_always_send_ehlo  =  no",  Postfix 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)

       Allow  DNS  CNAME  records  to override the servername that the Postfix
       SMTP  client  uses  for  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.

       This feature is available in Postfix 2.2.9 and later.

smtp_connect_timeout (default: 30s)

       The  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_reuse_limit (default: 10)

       When SMTP connection caching is enabled, the number of  times  that  an
       SMTP session may be reused before it is closed.

       This feature is available in Postfix 2.2. In Postfix 2.3 it is replaced
       by $smtp_connection_reuse_time_limit.

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_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  SMTP client time limit for sending the SMTP ".", and for receiving
       the 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 SMTP client time limit for sending the SMTP DATA command,  and  for
       receiving the 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 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:  Postfix 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_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.

       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  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  SMTP  client  time limit for sending the HELO or EHLO command, and
       for receiving the initial 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).

       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: 990)

       The maximal length of message header and body lines that  Postfix  will
       send via SMTP.  Longer lines are broken by inserting "<CR><LF><SPACE>".
       This minimizes the damage to MIME formatted mail.

       By default, the line length is limited to 990 characters, because  some
       server implementations cannot receive mail with long lines.

smtp_mail_timeout (default: 300s)

       The  SMTP  client time limit for sending the MAIL FROM command, and for
       receiving the 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 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 giving
       up or delivering 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_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 SMTP client time limit  for  sending  the  QUIT  command,  and  for
       receiving the 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 SMTP MAIL FROM and RCPT TO commands as  required  by
       RFC 2821. This includes putting quotes around an address localpart that
       ends in ".".

       The default is to comply with RFC 2821. 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  SMTP  client  time limit for sending the SMTP RCPT TO command, and
       for receiving the 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.

       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  SMTP  client  time  limit  for  sending  the RSET command, and for
       receiving the 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 further restricts what server mechanisms the
       client will take into consideration.

       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 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_xforward_command (default: no)

       Send the non-standard XFORWARD command when  the  Postfix  SMTP  server
       EHLO response announces XFORWARD support.

       This  allows  an  "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,  Postfix  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 SMTP servers that greet with a 4XX status code.

smtp_skip_5xx_greeting (default: yes)

       Skip SMTP servers that greet with a 5XX status code (go  away,  do  not
       try again later).

       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.  The default setting is incorrect, but it is what a lot of
       people expect to happen.

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.

       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.

       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 0.9.9 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 0.9.9 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  "fingerprint".   The
       fingerprint  is  a message digest of the server certificate. 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 fingerprint. The fingerprint  is  the
       message  digest of the server certificate 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 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

       This feature is available in Postfix 2.5 and later.

smtp_tls_key_file (default: $smtp_tls_cert_file)

       File with the Postfix SMTP client RSA private key in PEM format.   This
       file  may be combined with the Postfix SMTP client RSA certificate file
       specified with $smtp_tls_cert_file.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       Example:

       smtp_tls_key_file = $smtp_tls_cert_file

       This feature is available in Postfix 2.2 and later.

smtp_tls_loglevel (default: 0)

       Enable additional Postfix SMTP client logging of  TLS  activity.   Each
       logging  level  also includes the information that is logged at a lower
       logging level.

              0 Disable logging of TLS activity.

              1 Log TLS handshake and certificate information.

              2 Log levels during TLS negotiation.

              3 Log hexadecimal and ASCII dump of TLS negotiation process.

              4 Log hexadecimal and ASCII dump of complete transmission  after
              STARTTLS.

       Use "smtp_tls_loglevel = 3" only 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  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: SSLv3, TLSv1)

       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  is  expanded  to  support
       protocol  exclusions.  One  can now 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  still
       supported; use the form you find more intuitive.

       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:

       smtp_tls_mandatory_protocols = TLSv1
       # Alternative form with Postfix >= 2.5:
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3

       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.

       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  valid  "fingerprints"  of  the  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".

       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,  is  supported,  but  not recommended. OpenSSL provides no
       mechanisms for  excluding  protocols  not  known  at  compile-time.  If
       Postfix  is  linked against an OpenSSL library that supports additional
       protocol versions, they cannot be excluded using either syntax.

       Example:
       # TLSv1 only!
       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)

       The  server  certificate  peername verification method 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   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.

       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
              smtp_tls_fingerprint_cert_match   parameter   lists   the  valid
              "fingerprints" of the server certificate. The  digest  algorithm
              used   to   calculate   the   fingerprint  is  selected  by  the
              smtp_tls_fingerprint_digest parameter.

       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.

       This feature is available in Postfix 2.2 and later.

smtp_tls_verify_cert_match (default: hostname)

       The server certificate peername verification method  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  SMTP  client  time limit for sending the XFORWARD command, and for
       receiving the 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  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 SMTP clients are allowed to use the XCLIENT feature.  This command
       overrides 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 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 connection count,  connection  rate,  or
       SMTP   request   rate   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  SMTP  server  access  restrictions in the context of a client
       SMTP 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 client certificate fingerprint as  lookup  key  for  the
              specified  access(5)  database;  with  Postfix version 2.2, also
              require  that  the   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.

       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 all clients with a recognized  certificate
              would  be  allowed  to  relay.  This  feature  is available with
              Postfix version 2.2.

       permit_tls_clientcerts
              Permit the request  when  the  remote  SMTP  client  certificate
              fingerprint  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).  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.

       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).  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.

       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
              Change the meaning of the next restriction, so that  it  logs  a
              warning instead of rejecting a request (look for logfile records
              that contain "reject_warning"). This is useful for  testing  new
              restrictions in a "live" environment without risking unnecessary
              loss of mail.

       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.

       Postfix already implements a number of workarounds for malformed client
       commands.

       ·      Use "resolve_numeric_domain = yes" to accept "user@ipaddress".

       ·      Postfix already accepts the correct form "user@[ipaddress]".

       ·      Use   "strict_rfc821_envelopes   =  no"  to  accept  "User  Name
              <user@example.com>". Postfix will ignore the  "User  Name"  part
              before delivering the mail.

       Examples:

       /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

       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.

       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 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  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 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 syntax details.

smtpd_enforce_tls (default: no)

       Mandatory TLS: announce STARTTLS support to 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 off by default and should be used only on dedicated servers.

       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  SMTP  server  access  restrictions in the context of a client
       ETRN request.  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  causes 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, stress: 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 2.6 and later.

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  the  SMTP  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.

       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.

       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:  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_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: 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_invalid_helo_hostname       (with       Postfix      <      2.3:
       reject_invalid_hostname)
              Reject  the  request  when  the  HELO or EHLO hostname syntax is
              invalid.
              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 form, as required by the RFC.
              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 hostname is
              listed with the A record  "d.d.d.d"  under  rbl_domain  (Postfix
              version  2.1  and  later  only).  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.
              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).

       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, stress: 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  2.6
       and later.

smtpd_milters (default: empty)

       A  list  of Milter (mail filter) applications for new mail that arrives
       via the Postfix smtpd(8) server.  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_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: permit_mynetworks,

       reject_unauth_destination)
       The access restrictions that the Postfix SMTP  server  applies  in  the
       context  of  the  RCPT  TO  command.   See SMTPD_ACCESS_README, section
       "Delayed evaluation of SMTP access restriction lists" for a  discussion
       of evaluation context and time.

       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:  If  you  change this parameter setting, you must specify at
       least one of the following restrictions. Otherwise Postfix will  refuse
       to receive mail:

           reject, defer, defer_if_permit, reject_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).   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).

       reject_unknown_recipient_domain
              Reject the request when Postfix is not final destination for the
              recipient  domain,  and  the  RCPT  TO domain has no DNS A or MX
              record, or when it has 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 addres 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:

       smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination

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_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:

           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_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  the  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_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).  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 address has no  DNS  A  or  MX
              record,  or  when  it has 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  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_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: 300s)

       The time limit for Postfix SMTP server write and read operations during
       TLS startup and shutdown handshake procedures.

       This feature is available in Postfix 2.2 and later.

smtpd_timeout (default: normal: 300s, stress: 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  2.6  and
       later.

       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.

       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.

       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
       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
       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 command:

           openssl gendh -out /etc/postfix/dh_1024.pem -2 1024

       Your   actual   source  for  entropy  may  differ.  Some  systems  have
       /dev/random; on other  system  you  may  consider  using  the  "Entropy
       Gathering Daemon EGD", available at http://egd.sourceforge.net/

       Example:

       smtpd_tls_dh1024_param_file = /etc/postfix/dh_1024.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
       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 0.9.9 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 0.9.9 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  official  Postfix  releases
              (mail_version = major.minor.patchlevel).

       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  snapshot  releases  (mail_version   =
              major.minor-releasedate).

       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.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 0.9.9 or later.

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  used  to  construct client-certificate
       fingerprints for  check_ccert_access  and  permit_tls_clientcerts.  The
       default  algorithm  is  md5,  for  backwards compatibility with Postfix
       releases prior to 2.5.

       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

       Example: client-certificate access table, with sha1 fingerprints:

           /etc/postfix/main.cf:
               smtpd_tls_fingerprint_digest = sha1
               smtpd_client_restrictions =
                   check_ccert_access hash:/etc/postfix/access,
                   reject
           /etc/postfix/access:
               # Action folded to next line...
               AF:88:7C:AD:51:95:6F:36:96:F6:01:FB:2E:48:CD:AB:49:25:A2:3B
                   OK
               85:16:78:FD:73:6E:CE:70:E0:31:5F:0D:3C:C8:6D:C4:2C:24:59:E1
                   permit_auth_destination

       This feature is available in Postfix 2.5 and later.

smtpd_tls_key_file (default: $smtpd_tls_cert_file)

       File with the Postfix SMTP server RSA private key in PEM format.   This
       file  may be combined with the Postfix SMTP server RSA certificate file
       specified with $smtpd_tls_cert_file.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

smtpd_tls_loglevel (default: 0)

       Enable additional Postfix SMTP server logging of  TLS  activity.   Each
       logging  level  also includes the information that is logged at a lower
       logging level.

              0 Disable logging of TLS activity.

              1 Log TLS handshake and certificate information.

              2 Log levels during TLS negotiation.

              3 Log hexadecimal and ASCII dump of TLS negotiation process.

              4 Also log hexadecimal and ASCII dump of  complete  transmission
              after STARTTLS.

       Use  "smtpd_tls_loglevel = 3" only 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 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 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: SSLv3, TLSv1)

       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  is  expanded to support
       protocol exclusions. One can now 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 still
       supported, use the form you find more intuitive.

       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:

       smtpd_tls_mandatory_protocols = TLSv1
       # Alternative form with Postfix >= 2.5:
       smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3

       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.

       In main.cf the values are separated by whitespace, commas or colons. An
       empty  value  means allow all protocols. The valid protocol names, (see
       \fBfBSSL_get_version(3)),  are  "SSLv2",  "SSLv3"   and   "TLSv1".   In
       smtp_tls_policy_maps  table  entries,  "protocols" attribute values are
       separated by a colon.

       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,  is  supported,  but  not  recommended.  OpenSSL
       provides  no  mechanisms  for excluding protocols not known at compile-
       time. If Postfix is linked against an  OpenSSL  library  that  supports
       additional  protocol  versions,  they  cannot  be excluded using either
       syntax.

       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 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 SMTP clients,
              but do not require that clients use TLS encryption.

       encrypt
              Mandatory TLS encryption:  announce  STARTTLS  support  to  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 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.

       This feature is available in Postfix 2.2 and later.

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_use_tls (default: no)

       Opportunistic TLS: announce STARTTLS support to 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,  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.

       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_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_eecdh_strong_curve (default: prime256v1)

       The  elliptic  curve  used  by  the  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.

       This default curve is specified in  NSA  "Suite  B"  Cryptography  (see
       http://www.nsa.gov/ia/industry/crypto_suite_b.cfm)    for   information
       classified as 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.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 0.9.9 or later.

tls_eecdh_ultra_curve (default: secp384r1)

       The elliptic curve  used  by  the  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 specified in NSA "Suite B" Cryptography
       (see http://www.nsa.gov/ia/industry/crypto_suite_b.cfm) for information
       classified as TOP SECRET.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 0.9.9 or later.

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.

       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.

       This feature is available in Postfix 2.3 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.

       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.

       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_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.

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.

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.

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.

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.

       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.

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.

       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.

       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.

       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.

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.

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.

       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.

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.

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.

       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.

       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.

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: To: undisclosed-recipients:;)

       Message header that  the  Postfix  cleanup(8)  server  inserts  when  a
       message  contains  no  To:  or Cc: message header. With Postfix 2.4 and
       later, specify an empty value to disable this feature.

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
       2821.

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
       2821.

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
       2821.

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  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  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
       2821.

       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
       2821.

       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
       2821.

       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
       2821.

       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.

       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.

       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).

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 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  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.

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.

       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)