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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 deliv-
ery 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_do-
mains. 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_trans-
port, 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 de-
creasing precedence, the nexthop destination is taken from sender_dependent_de-
fault_transport_maps, default_transport, sender_dependent_relayhost_maps, relay-
host, 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 re-
build 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:
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 de-
scribed in section "TABLE SEARCH ORDER".
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_sub-
domains 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-daemon@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 de-
liver 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 informa-
tion.
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 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 AT example.com via the slow transport to a mail
exchanger for example.com. The slow transport could be configured to run at most one de-
livery 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 sub-
domains 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 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 AT example.com to host bar.example port 2025. Instead of a numeri-
cal 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 >= 3.5):
example.com smtp:bar.example, foo.example
This tries to deliver to bar.example before trying to deliver to foo.example.
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 AT anything.com 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 reg-
exp_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 reg-
ular 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_ta-
ble(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 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).
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
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA
TRANSPORT(5)
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On Apache
Under GNU General Public License
2025-02-21 10:23 @18.117.7.5 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)