TRANSPORT(5)

NAME
transport - format of Postfix transport table

SYNOPSIS
postmap /etc/postfix/transport

DESCRIPTION
The optional transport table specifies a mapping from domain hierarchies to message delivery transports and/or relay hosts. The mapping is used by the trivial-rewrite(8) daemon. Normally, the transport 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 in order to rebuild the indexed file after changing the 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. In that case, the lookups are done in a slightly different way as described below.

TABLE FORMAT
The format of the transport table is as follows:

pattern result
    When pattern matches the 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.

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:

domain transport:nexthop
    Mail for domain is delivered through transport to nexthop.

.domain transport:nexthop
    Mail for any subdomain of domain is delivered 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 subdomains.

Note: transport map entries take precedence over domains specified in the mydestination parameter. If you use the optional transport map, it may be safer to specify explicit entries for all domains specified in mydestination, for example:
hostname.my.domain local:
localhost.my.domain local: The interpretation of the nexthop field is transport dependent. In the case of SMTP, specify host:service for a non-default server port, and use [host] or [host]:port in order to disable MX (mail exchanger) DNS lookups. The [] form can also be used with IP addresses instead of hostnames.

EXAMPLES
In order to send mail for foo.org and its subdomains via the uucp transport to the UUCP host named foo:
foo.org uucp:foo
.foo.org uucp:foo When no nexthop host name is specified, the destination domain name is used instead. For example, the following directs mail for user@foo.org via the slow transport to a mail exchanger for foo.org. The slow transport could be something that runs at most one delivery process at a time:
foo.org slow: When no transport is specified, the default transport is used, as specified via the default_transport configuration parameter. The following sends all mail for foo.org and its subdomains to host gateway.foo.org:
foo.org :[gateway.foo.org]
.foo.org :[gateway.foo.org] In the above example, the [] are used to suppress MX lookups. The result would likely point to your local machine. In the case of delivery via SMTP, one may specify hostname:service instead of just a host:
foo.org smtp:bar.org:2025 This directs mail for user@foo.org to host bar.org port 2025. Instead of a numerical port a symbolic name may be used. Specify [] around the hostname in order to disable MX lookups. The error mailer can be used to bounce mail:
.foo.org error:mail for *.foo.org is not deliverable This causes all mail for user@anything.foo.org to be bounced.

REGULAR EXPRESSION TABLES
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 domain being looked up. Thus, some.domain.hierarchy is not broken up into parent domains. Patterns are applied in the order as specified in the table, until a pattern is found that matches the search string. Results are the same as with indexed file lookups, with the additional feature that parenthesized substrings from the pattern can be interpolated as $1, $2 and so on.

CONFIGURATION PARAMETERS
The following main.cf parameters are especially relevant to this topic. See the Postfix main.cf file for syntax details and for default values. Use the postfix reload command after a configuration change.

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

transport_maps
    List of transport lookup tables.

Other parameters of interest:

default_transport
    The transport to use when no transport is explicitly specified.

relayhost
    The default host to send to when no transport table entry matches.

SEE ALSO
postmap(1) create mapping table
trivial-rewrite(8) rewrite and resolve addresses
pcre_table(5) format of PCRE tables
regexp_table(5) format of POSIX regular expression tables

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