TRANSPORT(5) File Formats Manual TRANSPORT(5)
NAME
transport - Postfix transport table format
SYNOPSIS
postmap /etc/postfix/transport
postmap -q "string" /etc/postfix/transport
postmap -q - /etc/postfix/transport <inputfile
DESCRIPTION
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] desti‐
nations 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 nex‐
thop 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 TABLES" or "TCP-BASED TABLES".
CASE FOLDING
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.
TABLE FORMAT
The input format for the postmap(1) command is as follows:
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".
TABLE SEARCH ORDER
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 nexthop.
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 subdomains.
* transport:nexthop
The special pattern * represents any address (i.e. it functions as the wild-card pattern, and is unique
to Postfix transport tables).
Note 1: the null recipient address is looked up as $empty_address_recipient@$myhostname (default: mailer-dae‐
mon@hostname).
Note 2: user@domain or user+extension@domain lookup is available in Postfix 2.0 and later.
RESULT FORMAT
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 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 hostname.
A null transport and null nexthop result means "do not change": use the delivery transport and nexthop infor‐
mation 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
When no nexthop host name is specified, the destination domain name is used instead. For example, the follow‐
ing directs mail for [email protected] 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 DESCRIP‐
TION above). The following sends all mail for example.com and its subdomains to host gateway.example.com:
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 pri‐
mary 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 [email protected] 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 [email protected] to be bounced.
REGULAR EXPRESSION TABLES
This section describes how the table lookups change when the table is given in the form of regular expres‐
sions. 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
user@domain.
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).
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). 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.
CONFIGURATION PARAMETERS
The following main.cf parameters are especially relevant. The text below provides only a parameter summary.
SEE ALSO
trivial-rewrite(8), rewrite and resolve addresses
master(5), master.cf file format
postconf(5), configuration parameters
postmap(1), Postfix lookup table manager
README FILES
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
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
TRANSPORT(5)
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