TRANSPORT(5)

NAME
transport - format of Postfix transport table

SYNOPSIS
postmap /usr/local/etc/postfix/transport
postmap -q "string" /usr/local/etc/postfix/transport
postmap -q - /usr/local/etc/postfix/transport <inputfile

DESCRIPTION
The optional transport table specifies a mapping from email addresses to message delivery transports and/or relay hosts. The mapping is used by the trivial-rewrite(8) daemon. This mapping overrides the default routing that is built into Postfix:

mydestination
    A list of domains that is by default delivered via $local_transport.

virtual_mailbox_domains
    A list of domains that is by default delivered via $virtual_transport.

relay_domains
    A list of domains that is by default delivered via $relay_transport.

any other destination
    Mail for any other destination is by default delivered via $default_transport.

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 /usr/local/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, or lookups can be directed to TCP-based server. In that case, the lookups are done in a slightly different way as described below under "REGULAR EXPRESSION TABLES" and "TCP-BASED TABLES".

TABLE FORMAT
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. The transport field specifies a mail delivery transport such as smtp or local. The nexthop field specifies where and how to deliver mail. More details are given in section "RESULT FORMAT".

TABLE LOOKUP
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
    Mail for user+extension@domain is delivered through transport to nexthop.

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

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 1: the special pattern * represents any address (i.e. it functions as the wild-card pattern). Note 2: the null recipient address is looked up as $empty_address_recipient@$myhostname (default: mailer-daemon@hostname).

RESULT FORMAT
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 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 is required when you specify an IP address instead of a hostname. 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.

EXAMPLES
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 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, Postfix uses the transport that matches the address domain class (see TRANSPORT FIELD discussion above). 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 address being looked up. Thus, some.domain.hierarchy is not looked up up via its parent domains, nor is user+foo@domain looked up as user@domain. 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.

TCP-BASED TABLES
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). 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.

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.

empty_address_recipient
    The address that is looked up instead of the null sender address.

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.

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
tcp_table(5) TCP client/server table lookup protocol

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