Provided by: postfix_3.1.0-3ubuntu0.4_amd64 
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
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA
VIRTUAL(5)