ACCESS(5) File Formats Manual ACCESS(5)
NAME
access - Postfix SMTP server access table
SYNOPSIS
postmap /etc/postfix/access
postmap -q "string" /etc/postfix/access
postmap -q - /etc/postfix/access <inputfile
DESCRIPTION
This document describes access control on remote SMTP client information: host names, network addresses, and
envelope sender or recipient addresses; it is implemented by the Postfix SMTP server. See header_checks(5) or
body_checks(5) for access control on the content of email messages.
Normally, the access(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 com‐
mand "postmap /etc/postfix/access" to rebuild an indexed file after changing the corresponding text file.
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 cases, 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 action
When pattern matches a mail address, domain or host address, perform the corresponding action.
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.
EMAIL ADDRESS PATTERNS
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@domain
Matches the specified mail address.
domain.tld
Matches domain.tld as the domain part of an email address.
The pattern domain.tld also matches subdomains, but only when the string smtpd_access_maps is listed in
EMAIL ADDRESS EXTENSION
When a mail address localpart contains the optional recipient delimiter (e.g., user+foo@domain), the lookup
order becomes: user+foo@domain, user@domain, domain, user+foo@, and user@.
HOST NAME/ADDRESS PATTERNS
With lookups from indexed files such as DB or DBM, or from networked tables such as NIS, LDAP or SQL, the fol‐
lowing lookup patterns are examined in the order as listed:
domain.tld
Matches domain.tld.
The pattern domain.tld also matches subdomains, but only when the string smtpd_access_maps is listed in
the Postfix parent_domain_matches_subdomains configuration setting.
.domain.tld
Matches subdomains of domain.tld, but only when the string smtpd_access_maps is not listed in the Post‐
fix parent_domain_matches_subdomains configuration setting.
net.work.addr.ess
net.work.addr
net.work
net Matches the specified IPv4 host address or subnetwork. An IPv4 host address is a sequence of four deci‐
mal octets separated by ".".
Subnetworks are matched by repeatedly truncating the last ".octet" from the remote IPv4 host address
string until a match is found in the access table, or until further truncation is not possible.
NOTE 1: The access map lookup key must be in canonical form: do not specify unnecessary null charac‐
ters, and do not enclose network address information with "[]" characters.
NOTE 2: use the cidr lookup table type to specify network/netmask patterns. See cidr_table(5) for
details.
net:work:addr:ess
net:work:addr
net:work
net Matches the specified IPv6 host address or subnetwork. An IPv6 host address is a sequence of three to
eight hexadecimal octet pairs separated by ":".
Subnetworks are matched by repeatedly truncating the last ":octetpair" from the remote IPv6 host
address string until a match is found in the access table, or until further truncation is not possible.
NOTE 1: the truncation and comparison are done with the string representation of the IPv6 host address.
Thus, not all the ":" subnetworks will be tried.
NOTE 2: The access map lookup key must be in canonical form: do not specify unnecessary null charac‐
ters, and do not enclose network address information with "[]" characters.
REJECT ACTIONS
Postfix version 2.3 and later support enhanced status codes as defined in RFC 3463. When no code is specified
at the beginning of the text below, Postfix inserts a default enhanced status code of "5.7.1" in the case of
reject actions, and "4.7.1" in the case of defer actions. See "ENHANCED STATUS CODES" below.
4NN text
5NN text
Reject the address etc. that matches the pattern, and respond with the numerical three-digit code and
text. 4NN means "try again later", while 5NN means "do not try again".
The following responses have special meaning for the Postfix SMTP server:
421 text (Postfix 2.3 and later)
521 text (Postfix 2.6 and later)
After responding with the numerical three-digit code and text, disconnect immediately from the
SMTP client. This frees up SMTP server resources so that they can be made available to another
SMTP client.
Note: The "521" response should be used only with botnets and other malware where interoperabil‐
ity is of no concern. The "send 521 and disconnect" behavior is NOT defined in the SMTP stan‐
dard.
REJECT optional text...
Reject the address etc. that matches the pattern. Reply with "$access_map_reject_code optional text..."
when the optional text is specified, otherwise reply with a generic error response message.
DEFER optional text...
Reject the address etc. that matches the pattern. Reply with "$access_map_defer_code optional text..."
when the optional text is specified, otherwise reply with a generic error response message.
This feature is available in Postfix 2.6 and later.
DEFER_IF_REJECT optional text...
Defer the request if some later restriction would result in a REJECT action. Reply with
"$access_map_defer_code 4.7.1 optional text..." when the optional text is specified, otherwise reply
with a generic error response message.
Prior to Postfix 2.6, the SMTP reply code is 450.
This feature is available in Postfix 2.1 and later.
DEFER_IF_PERMIT optional text...
Defer the request if some later restriction would result in a an explicit or implicit PERMIT action.
Reply with "$access_map_defer_code 4.7.1 optional text..." when the optional text is specified, other‐
wise reply with a generic error response message.
Prior to Postfix 2.6, the SMTP reply code is 450.
This feature is available in Postfix 2.1 and later.
OTHER ACTIONS
restriction...
wise log a generic message.
Note: this action currently affects all recipients of the message. To discard only one recipient with‐
out discarding the entire message, use the transport(5) table to direct mail to the discard(8) service.
This feature is available in Postfix 2.0 and later.
DUNNO Pretend that the lookup key was not found. This prevents Postfix from trying substrings of the lookup
key (such as a subdomain name, or a network address subnetwork).
This feature is available in Postfix 2.0 and later.
FILTER transport:destination
After the message is queued, send the entire message through the specified external content filter. The
transport name specifies the first field of a mail delivery agent definition in master.cf; the syntax
of the next-hop destination is described in the manual page of the corresponding delivery agent. More
information about external content filters is in the Postfix FILTER_README file.
Note 1: do not use $number regular expression substitutions for transport or destination unless you
know that the information has a trusted origin.
Note 2: this action overrides the main.cf content_filter setting, and affects all recipients of the
message. In the case that multiple FILTER actions fire, only the last one is executed.
Note 3: the purpose of the FILTER command is to override message routing. To override the recipient's
transport but not the next-hop destination, specify an empty filter destination (Postfix 2.7 and
later), or specify a transport:destination that delivers through a different Postfix instance (Postfix
2.6 and earlier). Other options are using the recipient-dependent transport_maps or the sen‐
der-dependent sender_dependent_default_transport_maps features.
This feature is available in Postfix 2.0 and later.
HOLD optional text...
Place the message on the hold queue, where it will sit until someone either deletes it or releases it
for delivery. Log the optional text if specified, otherwise log a generic message.
Mail that is placed on hold can be examined with the postcat(1) command, and can be destroyed or
released with the postsuper(1) command.
Note: use "postsuper -r" to release mail that was kept on hold for a significant fraction of $maxi‐
mal_queue_lifetime or $bounce_queue_lifetime, or longer. Use "postsuper -H" only for mail that will not
expire within a few delivery attempts.
Note: this action currently affects all recipients of the message.
This feature is available in Postfix 2.0 and later.
PREPEND headername: headervalue
Prepend the specified message header to the message. When more than one PREPEND action executes, the
first prepended header appears before the second etc. prepended header.
Note: this action must execute before the message content is received; it cannot execute in the context
of smtpd_end_of_data_restrictions.
sender, recipient and protocol information.
This feature is available in Postfix 2.1 and later.
ENHANCED STATUS CODES
Postfix version 2.3 and later support enhanced status codes as defined in RFC 3463. When an enhanced status
code is specified in an access table, it is subject to modification. The following transformations are needed
when the same access table is used for client, helo, sender, or recipient access restrictions; they happen
regardless of whether Postfix replies to a MAIL FROM, RCPT TO or other SMTP command.
· When a sender address matches a REJECT action, the Postfix SMTP server will transform a recipient DSN
status (e.g., 4.1.1-4.1.6) into the corresponding sender DSN status, and vice versa.
· When non-address information matches a REJECT action (such as the HELO command argument or the client
hostname/address), the Postfix SMTP server will transform a sender or recipient DSN status into a
generic non-address DSN status (e.g., 4.0.0).
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 string being looked up. Depending on the
application, that string is an entire client hostname, an entire client IP address, or an entire mail address.
Thus, no parent domain or parent network search is done, user@domain mail addresses are not broken up into
their user@ and domain constituent parts, nor is user+foo broken up into user and foo.
Patterns are applied in the order as specified in the table, until a pattern is found that matches the search
string.
Actions 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). This feature is not available up to
and including Postfix version 2.4.
Each lookup operation uses the entire query string once. Depending on the application, that string is an
entire client hostname, an entire client IP address, or an entire mail address. Thus, no parent domain or
parent network search is done, user@domain mail addresses are not broken up into their user@ and domain con‐
stituent parts, nor is user+foo broken up into user and foo.
Actions are the same as with indexed file lookups.
EXAMPLE
The following example uses an indexed file, so that the order of table entries does not matter. The example
permits access by the client at address 1.2.3.4 but rejects all other clients in 1.2.3.0/24. Instead of hash
lookup tables, some systems use dbm. Use the command "postconf -m" to find out what lookup tables Postfix
supports on your system.
/etc/postfix/main.cf:
smtpd_client_restrictions =
check_client_access hash:/etc/postfix/access
postconf(5), configuration parameters
transport(5), transport:nexthop syntax
README FILES
Use "postconf readme_directory" or "postconf html_directory" to locate this information.
SMTPD_ACCESS_README, built-in SMTP server access control
DATABASE_README, Postfix lookup table overview
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
ACCESS(5)
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