virtual (5)

Contents

NAME
SYNOPSIS
DESCRIPTION
CASE FOLDING
TABLE FORMAT
TABLE SEARCH ORDER
RESULT ADDRESS REWRITING
ADDRESS EXTENSION
VIRTUAL ALIAS DOMAINS
REGULAR EXPRESSION TABLES
TCP-BASED TABLES
BUGS
CONFIGURATION PARAMETERS
SEE ALSO
README FILES
LICENSE
AUTHOR(S)

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, patterns are tried in the order as
listed below:



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.




SEE ALSO




cleanup(8), canonicalize and enqueue mail
postmap(1), Postfix lookup table manager
postconf(5), configuration parameters
canonical(5), canonical address mapping



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