access

access - Postfix SMTP server access table

postmap /etc/postfix/access

postmap -q "string" /etc/postfix/access

postmap -q - /etc/postfix/access <inputfile

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 command "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".

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:

"pattern When pattern matches a mail address, domain or host address, perform the corresponding action.

"blank Empty lines and whitespace-only lines are ignored, as are lines whose first non-whitespace character is a `#'.

"multi-line A logical line starts with non-whitespace text. A line that starts with whitespace continues a logical line.

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 the Postfix parent_domain_matches_subdomains configuration setting (note that this is the default for some versions of Postfix). Otherwise, specify .domain.tld (note the initial dot) in order to match subdomains.

user@ Matches all mail addresses with the specified user part.

Note: lookup of the null sender address is not possible with some types of lookup table. By default, Postfix uses <> as the lookup key for such addresses. The value is specified with the smtpd_null_access_lookup_key parameter in the Postfix main.cf file.

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@.

With lookups from indexed files such as DB or DBM, or from networked tables such as NIS, LDAP or SQL, the following 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. Otherwise, specify .domain.tld (note the initial dot) in order to match subdomains.

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 decimal 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 characters, 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 characters, and do not enclose network address information with "[]" characters. NOTE 3: use the cidr lookup table type to specify network/netmask patterns. See cidr_table(5) for details. IPv6 support is available in Postfix 2.2 and later.

OK Accept the address etc. that matches the pattern.

all-numerical An all-numerical result is treated as OK. This format is generated by address-based relay authorization schemes such as pop-before-smtp.

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

"5NN 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 reply code "421" causes Postfix to disconnect immediately (Postfix version 2.3 and later).

"REJECT Reject the address etc. that matches the pattern. Reply with $reject_code optional text... when the optional text is specified, otherwise reply with a generic error response message.

"DEFER_IF_REJECT Defer the request if some later restriction would result in a REJECT action. Reply with "450 4.7.1 optional text... when the optional text is specified, otherwise reply with a generic error response message. This feature is available in Postfix 2.1 and later.

"DEFER_IF_PERMIT Defer the request if some later restriction would result in a an explicit or implicit PERMIT action. Reply with "450 4.7.1 optional text... when the optional text is specified, otherwise reply with a generic error response message. This feature is available in Postfix 2.1 and later.

restriction... Apply the named UCE restriction(s) (permit, reject, reject_unauth_destination, and so on).

"DISCARD Claim successful delivery and silently discard the message. Log the optional text if specified, otherwise log a generic message. Note: this action currently affects all recipients of the message. To discard only one recipient without 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 After the message is queued, send the entire message through the specified external content filter. The transport:destination syntax is described in the transport(5) manual page. More information about external content filters is in the Postfix FILTER_README file. Note: this action overrides the content_filter setting, and currently affects all recipients of the message. This feature is available in Postfix 2.0 and later.

"HOLD 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 $maximal_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 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. This feature is available in Postfix 2.1 and later.

"REDIRECT After the message is queued, send the message to the specified address instead of the intended recipient(s). Note: this action overrides the FILTER action, and currently affects all recipients of the message. This feature is available in Postfix 2.1 and later.

"WARN Log a warning with the optional text, together with client information and if available, with helo, sender, recipient and protocol information. This feature is available in Postfix 2.1 and later.

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).

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 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.

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 constituent parts, nor is user+foo broken up into user and foo. Actions are the same as with indexed file lookups.

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

/etc/postfix/access:
    1.2.3   REJECT
    1.2.3.4 OK

Execute the command "postmap /etc/postfix/access" after editing the file.

The table format does not understand quoting conventions.

postmap(1), Postfix lookup table manager
smtpd(8), SMTP server
postconf(5), configuration parameters
transport(5), transport:nexthop syntax

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

The Secure Mailer license must be distributed with this software.

Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA