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man pages section 5: File Formats

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Updated: Wednesday, February 9, 2022

transport (5)


transport - Postfix transport table format


postmap /etc/postfix/transport

postmap -q "string" /etc/postfix/transport

postmap -q - /etc/postfix/transport <inputfile


TRANSPORT(5)                  File Formats Manual                 TRANSPORT(5)

       transport - Postfix transport table format

       postmap /etc/postfix/transport

       postmap -q "string" /etc/postfix/transport

       postmap -q - /etc/postfix/transport <inputfile

       The   optional  transport(5)  table  specifies  a  mapping  from  email
       addresses to message delivery  transports  and  next-hop  destinations.
       Message  delivery  transports  such as local or smtp are defined in the
       master.cf file, and next-hop destinations are typically hosts or domain
       names. The table is searched by the trivial-rewrite(8) daemon.

       This  mapping overrides the default transport:nexthop selection that is
       built into Postfix:

       local_transport (default: local:$myhostname)
              This is the default for final delivery to  domains  listed  with
              mydestination,  and  for  [ipaddress]  destinations  that  match
              $inet_interfaces or $proxy_interfaces. The default nexthop  des-
              tination is the MTA hostname.

       virtual_transport (default: virtual:)
              This  is  the  default for final delivery to domains listed with
              virtual_mailbox_domains. The default nexthop destination is  the
              recipient domain.

       relay_transport (default: relay:)
              This  is  the default for remote delivery to domains listed with
              relay_domains. In order of decreasing  precedence,  the  nexthop
              destination   is   taken   from  relay_transport,  sender_depen-
              dent_relayhost_maps, relayhost, or from the recipient domain.

       default_transport (default: smtp:)
              This is the default for remote delivery to  other  destinations.
              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.

       Normally, the transport(5) table is  specified  as  a  text  file  that
       serves as input to the postmap(1) command.  The result, an indexed file
       in dbm or db format, is used for fast searching  by  the  mail  system.
       Execute  the  command  "postmap  /etc/postfix/transport"  to rebuild an
       indexed file after changing the corresponding transport table.

       When the table is provided via other means such as NIS,  LDAP  or  SQL,
       the same lookups are done as for ordinary indexed files.

       Alternatively,  the  table  can be provided as a regular-expression map
       where patterns are given as regular  expressions,  or  lookups  can  be
       directed  to TCP-based server. In those case, the lookups are done in a
       slightly different way as described  below  under  "REGULAR  EXPRESSION

       The  search string is folded to lowercase before database lookup. As of
       Postfix 2.3, the search string is not case folded with  database  types
       such  as  regexp: or pcre: whose lookup fields can match both upper and
       lower case.

       The input format for the postmap(1) command is as follows:

       pattern result
              When pattern matches the recipient address or  domain,  use  the
              corresponding result.

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

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

       The pattern specifies an email address, a domain name, or a domain name
       hierarchy, as described in section "TABLE LOOKUP".

       The result is of the form transport:nexthop and specifies how or  where
       to deliver mail. This is described in section "RESULT FORMAT".

       With  lookups  from  indexed files such as DB or DBM, or from networked
       tables such as NIS, LDAP or SQL, patterns are tried  in  the  order  as
       listed below:

       user+extension@domain transport:nexthop
              Deliver mail for user+extension@domain through transport to nex-

       user@domain transport:nexthop
              Deliver mail for user@domain through transport to nexthop.

       domain transport:nexthop
              Deliver mail for domain through transport to nexthop.

       .domain transport:nexthop
              Deliver mail for any subdomain of domain  through  transport  to
              nexthop. This applies only when the string transport_maps is not
              listed  in  the  parent_domain_matches_subdomains  configuration
              setting.  Otherwise, a domain name matches itself and its subdo-

       * transport:nexthop
              The special pattern * represents any address (i.e. it  functions
              as  the  wild-card  pattern,  and is unique to Postfix transport

       Note   1:   the   null   recipient   address   is    looked    up    as
       $empty_address_recipient@$myhostname (default: mailer-daemon@hostname).

       Note  2:  user@domain  or  user+extension@domain lookup is available in
       Postfix 2.0 and later.

       The lookup result is of  the  form  transport:nexthop.   The  transport
       field  specifies  a  mail delivery transport such as smtp or local. The
       nexthop field specifies where and how to deliver mail.

       The transport field specifies the name of  a  mail  delivery  transport
       (the  first  name  of a mail delivery service entry in the Postfix mas-
       ter.cf file).

       The interpretation of the nexthop field is transport dependent. In  the
       case  of SMTP, specify a service on a non-default port as host:service,
       and disable MX (mail exchanger) DNS lookups with [host] or [host]:port.
       The  []  form  is  required when you specify an IP address instead of a

       A null transport and null nexthop result means "do not change": use the
       delivery  transport and nexthop information that would be used when the
       entire transport table did not exist.

       A non-null transport field with a null nexthop field resets the nexthop
       information to the recipient domain.

       A  null transport field with non-null nexthop field does not modify the
       transport information.

       In order to deliver internal mail directly, while using  a  mail  relay
       for  all other mail, specify a null entry for internal destinations (do
       not change the delivery transport or the nexthop information) and spec-
       ify a wildcard for all other destinations.

            my.domain    :
            .my.domain   :
            *            smtp:outbound-relay.my.domain

       In  order  to send mail for example.com and its subdomains via the uucp
       transport to the UUCP host named example:

            example.com      uucp:example
            .example.com     uucp:example

       When no nexthop host name is specified, the destination domain name  is
       used  instead.  For  example, the following directs mail for user@exam-
       ple.com via the slow transport to a  mail  exchanger  for  example.com.
       The  slow  transport  could  be  configured to run at most one delivery
       process at a time:

            example.com      slow:

       When no transport is specified, Postfix uses the transport that matches
       the  address domain class (see DESCRIPTION above).  The following sends
       all mail for example.com  and  its  subdomains  to  host  gateway.exam-

            example.com      :[gateway.example.com]
            .example.com     :[gateway.example.com]

       In  the  above example, the [] suppress MX lookups.  This prevents mail
       routing loops when your machine is primary MX host for example.com.

       In the case of delivery via  SMTP,  one  may  specify  hostname:service
       instead of just a host:

            example.com      smtp:bar.example:2025

       This  directs  mail for user@example.com to host bar.example port 2025.
       Instead of a numerical port a symbolic name may  be  used.  Specify  []
       around the hostname if MX lookups must be disabled.

       The error mailer can be used to bounce mail:

            .example.com     error:mail for *.example.com is not deliverable

       This causes all mail for user@anything.example.com to be bounced.

       This  section  describes how the table lookups change when the table is
       given in the form of regular expressions. For a description of  regular
       expression lookup table syntax, see regexp_table(5) or pcre_table(5).

       Each  pattern  is  a  regular  expression that is applied to the entire
       address being looked up. Thus, some.domain.hierarchy is not  looked  up
       via   its   parent   domains,  nor  is  user+foo@domain  looked  up  as

       Patterns are applied in the order as specified in the  table,  until  a
       pattern is found that matches the search string.

       The trivial-rewrite(8) server disallows regular expression substitution
       of $1 etc. in regular expression lookup tables, because that could open
       a security hole (Postfix version 2.3 and later).

       This  section  describes  how the table lookups change when lookups are
       directed  to  a  TCP-based  server.  For  a  description  of  the   TCP
       client/server  lookup  protocol, see tcp_table(5).  This feature is not
       available up to and including Postfix version 2.4.

       Each lookup operation uses the entire recipient  address  once.   Thus,
       some.domain.hierarchy  is  not looked up via its parent domains, nor is
       user+foo@domain looked up as user@domain.

       Results are the same as with indexed file lookups.

       The following main.cf parameters are  especially  relevant.   The  text
       below  provides  only  a  parameter  summary.  See postconf(5) for more
       details including examples.

              The address that  is  looked  up  instead  of  the  null  sender

              List  of  Postfix features that use domain.tld patterns to match
              sub.domain.tld (as opposed to requiring .domain.tld patterns).

              List of transport lookup tables.

       See attributes(7) for descriptions of the following attributes:

       |ATTRIBUTE TYPE |       ATTRIBUTE VALUE        |
       |Availability   | service/network/smtp/postfix |
       |Stability      | Volatile                     |

       trivial-rewrite(8), rewrite and resolve addresses
       master(5), master.cf file format
       postconf(5), configuration parameters
       postmap(1), Postfix lookup table manager

       Use "postconf readme_directory" or "postconf html_directory" to  locate
       this information.
       ADDRESS_REWRITING_README, address rewriting guide
       DATABASE_README, Postfix lookup table overview
       FILTER_README, external content filter

       The Secure Mailer license must be distributed with this software.

       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA

       Source code for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This software was built from source available at
       https://github.com/oracle/solaris-userland.  The original community
       source was downloaded from  https://archive.mgm51.com/mirrors/postfix-

       Further information about this software can be found on the open source
       community website at http://www.postfix.org.