Updated: 2021/Apr/14

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
              destination 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_dependent_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

       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

       * 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
       master.cf file).

       The nexthop field usually specifies one recipient domain or hostname.
       In the case of the Postfix SMTP/LMTP client, the nexthop field may
       contain a list of nexthop destinations separated by comma or whitespace
       (Postfix 3.5 and later).

       The syntax of a nexthop destination is transport dependent.  With 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 hostname.

       A null transport and null nexthop field 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
       specify 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@example.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

            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 or LMTP, one may specify host: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.

       Deliveries via SMTP or LMTP support multiple destinations (Postfix >=

            example.com      smtp:bar.example, foo.example

       This tries to deliver to bar.example before trying to deliver to

       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.

       empty_address_recipient (MAILER-DAEMON)
              The recipient of mail addressed to the null address.

       parent_domain_matches_subdomains (see 'postconf -d' output)
              A list of Postfix features where the pattern "example.com" also
              matches subdomains of example.com, instead of requiring an
              explicit ".example.com" pattern.

       transport_maps (empty)
              Optional lookup tables with mappings from recipient address to
              (message delivery transport, next-hop destination).

       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