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You are here: manpages

VIRTUAL

Section: File Formats (5)
Index Return to Main Contents

NAME

virtual - Postfix virtual alias table format

SYNOPSIS

postmap /etc/postfix/virtual

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

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

DESCRIPTION

The optional virtual(5) alias table rewrites recipient addresses for all local, all virtual, and all remote mail destinations. This is unlike the aliases(5) table which is used only for local(8) delivery. Virtual aliasing is recursive, and is implemented by the Postfix cleanup(8) daemon before mail is queued.

The main applications of virtual aliasing are:

*: To redirect mail for one address to one or more addresses.
*: To implement virtual alias domains where all addresses are aliased to addresses in other domains.
Virtual alias domains are not to be confused with the virtual mailbox domains that are implemented with the Postfix virtual(8) mail delivery agent. With virtual mailbox domains, each recipient address can have its own mailbox.

Virtual aliasing is applied only to recipient envelope addresses, and does not affect message headers. Use canonical(5) mapping to rewrite header and envelope addresses in general.

Normally, the virtual(5) alias 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" 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 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 address, address, ...: When pattern matches a mail address, replace it by the corresponding address.
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.

TABLE SEARCH ORDER

With lookups from indexed files such as DB or DBM, or from networked tables such as NIS, LDAP or SQL, each user@domain query produces a sequence of query patterns as described below.

Each query pattern is sent to each specified lookup table before trying the next query pattern, until a match is found.

user@domain address, address, ...: Redirect mail for user@domain to address. This form has the highest precedence.
user address, address, ...: Redirect mail for user@site to address when site is equal to $myorigin, when site is listed in $mydestination, or when it is listed in $inet_interfaces or $proxy_interfaces.
This functionality overlaps with functionality of the local aliases(5) database. The difference is that virtual(5) mapping can be applied to non-local addresses.
@domain address, address, ...: Redirect mail for other users in domain to address. This form has the lowest precedence.
Note: @domain is a wild-card. With this form, the Postfix SMTP server accepts mail for any recipient in domain, regardless of whether that recipient exists. This may turn your mail system into a backscatter source: Postfix first accepts mail for non-existent recipients and then tries to return that mail as "undeliverable" to the often forged sender address.

RESULT ADDRESS REWRITING

The lookup result is subject to address rewriting:

*: When the result has the form @otherdomain, the result becomes the same user in otherdomain. This works only for the first address in a multi-address lookup result.
*: When "append_at_myorigin=yes", append "@$myorigin" to addresses without "@domain".
*: When "append_dot_mydomain=yes", append ".$mydomain" to addresses without ".domain".

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.

The propagate_unmatched_extensions parameter controls whether an unmatched address extension (+foo) is propagated to the result of table lookup.

VIRTUAL ALIAS DOMAINS

Besides virtual aliases, the virtual alias table can also be used to implement virtual alias domains. With a virtual alias domain, all recipient addresses are aliased to addresses in other domains.

Virtual alias domains are not to be confused with the virtual mailbox domains that are implemented with the Postfix virtual(8) mail delivery agent. With virtual mailbox domains, each recipient address can have its own mailbox.

With a virtual alias domain, the virtual domain has its own user name space. Local (i.e. non-virtual) usernames are not visible in a virtual alias domain. In particular, local aliases(5) and local mailing lists are not visible as localname@virtual-alias.domain.

Support for a virtual alias domain looks like:

/etc/postfix/main.cf:
    virtual_alias_maps = hash:/etc/postfix/virtual

Note: some systems use dbm databases instead of hash. See the output from "postconf -m" for available database types.

/etc/postfix/virtual:
    virtual-alias.domain    anything (right-hand content does not matter)
    postmaster@virtual-alias.domain postmaster
    user1@virtual-alias.domain      address1
    user2@virtual-alias.domain      address2, address3

The virtual-alias.domain anything entry is required for a virtual alias domain. Without this entry, mail is rejected with "relay access denied", or bounces with "mail loops back to myself".

Do not specify virtual alias domain names in the main.cf mydestination or relay_domains configuration parameters.

With a virtual alias domain, the Postfix SMTP server accepts mail for known-user@virtual-alias.domain, and rejects mail for unknown-user@virtual-alias.domain as undeliverable.

Instead of specifying the virtual alias domain name via the virtual_alias_maps table, you may also specify it via the main.cf virtual_alias_domains configuration parameter. This latter parameter uses the same syntax as the main.cf mydestination configuration parameter.

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, 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 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 address once. 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.

Results are the same as with indexed file lookups.

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_alias_maps: List of virtual aliasing tables.
virtual_alias_domains: List of virtual alias domains. This uses the same syntax as the mydestination parameter.
propagate_unmatched_extensions: A list of address rewriting or forwarding mechanisms that propagate an address extension from the original address to the result. Specify zero or more of canonical, virtual, alias, forward, include, or generic.

Other parameters of interest:

inet_interfaces: The network interface addresses that this system receives mail on. You need to stop and start Postfix when this parameter changes.
mydestination: List of domains that this mail system considers local.
myorigin: The domain that is appended to any address that does not have a domain.
owner_request_special: Give special treatment to owner-xxx and xxx-request addresses.
proxy_interfaces: Other interfaces that this machine receives mail on by way of a proxy agent or network address translator.

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
VIRTUAL_README, domain hosting guide

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