transport - Postfix transport table format
postmap -q "string" /etc/postfix/transport
postmap -q - /etc/postfix/transport <inputfile
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_mail-
box_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_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
decreasing precedence, the nexthop destination is taken from sender_depen-
dent_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".
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.
The input format for the postmap(1) command is as follows:
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 `#'.
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 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:
Deliver mail for user+extension@domain through transport to nexthop.
Deliver mail for user@domain through transport to nexthop.
Deliver mail for domain through transport to 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
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
Note 2: user@domain or user+extension@domain lookup is available in Postfix 2.0 and later.
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
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, spec-
ify 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 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
A null transport field with non-null nexthop field does not modify the transport informa-
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.
In order to send mail for example.com and its subdomains via the uucp transport to the
UUCP host named example:
When no nexthop host name is specified, the destination domain name is used instead. For
example, the following directs mail for email@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:
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:
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, one may specify hostname:service instead of just a host:
This directs mail for firstname.lastname@example.org 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
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@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 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).
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.
The following main.cf parameters are especially relevant. The text below provides only a
parameter summary. See postconf(5) for more details including examples.
The address that is looked up instead of the null sender address.
List of Postfix features that use domain.tld patterns to match sub.domain.tld (as
opposed to requiring .domain.tld patterns).
List of transport lookup tables.
trivial-rewrite(8), rewrite and resolve addresses
master(5), master.cf file format
postconf(5), configuration parameters
postmap(1), Postfix lookup table manager
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
The Secure Mailer license must be distributed with this software.
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA