Updated: 2022/Sep/29
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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 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 a 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 described 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_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-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 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.
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@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
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@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 >=
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@anything.example.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 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 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)