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Sendmail Masquerading
11-16-2006
Sendmail Masquerading
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VIRTUAL(5) File Formats Manual VIRTUAL(5) NAME
virtual - format of Postfix virtual table SYNOPSIS
postmap /etc/postfix/virtual DESCRIPTION
The optional virtual table specifies address redirections for local and non-local recipients or domains. The redirections are used by the cleanup(8) daemon. The redirections are recursive. The virtual redirection is applied only to recipient envelope addresses, and does not affect message headers. Think Sendmail rule set S0, if you like. Use canonical(5) mapping to rewrite header and envelope addresses in general. Normally, the virtual 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/virtual in order to rebuild the indexed file after changing the 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. In that case, the lookups are done in a slightly different way as described below. POSTFIX-STYLE VIRTUAL DOMAINS With a Postfix-style virtual domain, the virtual domain has its own user name space. Local (i.e. non-virtual) usernames are not visible in a Postfix-style virtual domain. In particular, local aliases(5) and mailing lists are not visible as localname@virtual.domain. Use a Sendmail-style virtual domain (see below) if local usernames, aliases(5) or mailing lists should be visible as localname@vir- tual.domain. Support for a Postfix-style virtual domain looks like: /etc/postfix/virtual: virtual.domain anything (right-hand content does not matter) postmaster@virtual.domain postmaster user1@virtual.domain address1 user2@virtual.domain address2, address3 The virtual.domain anything entry is required for a Postfix-style virtual domain. Do not list a Postfix-style virtual domain in the main.cf mydestination configuration parameter. Such an entry is required only for a Sendmail-style virtual domain. With a Postfix-style virtual domain, the Postfix SMTP server accepts mail for known-user@virtual.domain and rejects mail for unknown- user@virtual.domain as undeliverable. SENDMAIL-STYLE VIRTUAL DOMAINS With a Sendmail-style virtual domain, every local (i.e. non-virtual) username is visible in the virtual domain. In particular, every local alias and mailing list is visible as localname@virtual.domain. Use a Postfix-style virtual domain (see above) if local usernames, aliases(5) or mailing lists should not be visible as localname@vir- tual.domain. Support for a Sendmail-style virtual domain looks like: /etc/postfix/main.cf: mydestination = $myhostname localhost.$mydomain $mydomain virtual.domain /etc/postfix/virtual: user1@virtual.domain address1 user2@virtual.domain address2, address3 The main.cf mydestination entry is required for a Sendmail-style virtual domain. Do not specify a virtual.domain anything virtual map entry for a Sendmail-style virtual domain. Such an entry is required only with a Postfix-style virtual domain. With a Sendmail-style virtual domain, the Postfix local delivery agent delivers mail for an unknown user@virtual.domain to a local (i.e. non-virtual) user that has the same name; if no such recipient exists, the Postfix local delivery agent bounces the mail to the sender. TABLE FORMAT
The format of the virtual table is as follows, mappings being tried in the order as listed in this manual page: pattern result When pattern matches a mail address, replace it by 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. 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 address, address, ... Mail for user@domain is redirected to address. This form has the highest precedence. user address, address, ... Mail for user@site is redirected to address when site is equal to $myorigin, when site is listed in $mydestination, or when it is listed in $inet_interfaces. This functionality overlaps with functionality of the local alias(5) database. The difference is that virtual mapping can be applied to non-local addresses. @domain address, address, ... Mail for any user in domain is redirected to address. This form has the lowest precedence. In all the above forms, when address has the form @otherdomain, the result is the same user in otherdomain. This works for the first address in the expansion only. 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, user+foo, user, and @domain. An unmatched address extension (+foo) is propagated to the result of table lookup. 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 regu- lar 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, 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. Results are the same as with indexed file lookups, with the additional feature that parenthesized substrings from the pattern can be inter- polated as $1, $2 and so on. BUGS
The table format does not understand quoting conventions. CONFIGURATION PARAMETERS
The following main.cf parameters are especially relevant to this topic. See the Postfix main.cf file for syntax details and for default values. Use the postfix reload command after a configuration change. virtual_maps List of virtual mapping tables. Other parameters of interest: inet_interfaces The network interface addresses that this system receives mail on. mydestination List of domains that this mail system considers local. myorigin The domain that is appended to locally-posted mail. owner_request_special Give special treatment to owner-xxx and xxx-request addresses. SEE ALSO
cleanup(8) canonicalize and enqueue mail postmap(1) create mapping table pcre_table(5) format of PCRE tables regexp_table(5) format of POSIX regular expression tables 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 VIRTUAL(5)