VIRTUAL(5) VIRTUAL(5)
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:
o To redirect mail for one address to one or more
addresses.
o 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 expres-
sions, 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 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 logi-
cal 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 $mydes-
tination, or when it is listed in $inet_interfaces
or $proxy_interfaces.
This functionality overlaps with functionality of
the local aliases(5) database. The difference is
that virtual(5) mapping can be applied to non-local
addresses.
@domain address, address, ...
Redirect mail for other users in domain to address.
This form has the lowest precedence.
Note: @domain is a wild-card. With this form, the
Postfix SMTP server accepts mail for any recipient
in domain, regardless of whether that recipient
exists. This may turn your mail system into a
backscatter source: Postfix first accepts mail for
non-existent recipients and then tries to return
that mail as "undeliverable" to the often forged
sender address.
RESULT ADDRESS REWRITING
The lookup result is subject to address rewriting:
o When the result has the form @otherdomain, the
result becomes the same user in otherdomain. This
works only for the first address in a multi-address
lookup result.
o When "append_at_myorigin=yes", append "@$myorigin"
to addresses without "@domain".
o When "append_dot_mydomain=yes", append ".$mydomain"
to addresses without ".domain".
ADDRESS EXTENSION
When a mail address localpart contains the optional recip-
ient 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 propa-
gated 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 vir-
tual 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 ta-
ble, 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 descrip-
tion of the TCP client/server lookup protocol, see tcp_ta-
ble(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 mecha-
nisms 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 Post-
fix 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 transla-
tor.
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
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
VIRTUAL(5)