.\"	$NetBSD: virtual.5,v 1.4.2.1 2023/12/25 12:43:27 martin Exp $
.\"
.TH VIRTUAL 5 
.ad
.fi
.SH NAME
virtual
\-
Postfix virtual alias table format
.SH "SYNOPSIS"
.na
.nf
\fBpostmap /etc/postfix/virtual\fR

\fBpostmap \-q "\fIstring\fB" /etc/postfix/virtual\fR

\fBpostmap \-q \- /etc/postfix/virtual <\fIinputfile\fR
.SH DESCRIPTION
.ad
.fi
The optional \fBvirtual\fR(5) alias table rewrites recipient
addresses for all local, all virtual, and all remote mail
destinations.
This is unlike the \fBaliases\fR(5) table which is used
only for \fBlocal\fR(8) delivery. This feature is implemented
in the Postfix \fBcleanup\fR(8) daemon before mail is queued.

Virtual aliasing is recursive; to terminate recursion for
a specific address, alias that address to itself.

The main applications of virtual aliasing are:
.IP \(bu
To redirect mail for one address to one or more addresses.
.IP \(bu
To implement virtual alias domains where all addresses are aliased
to addresses in other domains.
.sp
Virtual alias domains are not to be confused with the virtual mailbox
domains that are implemented with the Postfix \fBvirtual\fR(8) mail
delivery agent. With virtual mailbox domains, each recipient address
can have its own mailbox.
.PP
Virtual aliasing is applied only to recipient
envelope addresses, and does not affect message headers.
Use \fBcanonical\fR(5)
mapping to rewrite header and envelope addresses in general.

Normally, the \fBvirtual\fR(5) alias table is specified as a text file
that serves as input to the \fBpostmap\fR(1) command.
The result, an indexed file in \fBdbm\fR or \fBdb\fR format,
is used for fast searching by the mail system. Execute the command
"\fBpostmap /etc/postfix/virtual\fR" 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 a 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".
.SH "CASE FOLDING"
.na
.nf
.ad
.fi
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.
.SH "TABLE FORMAT"
.na
.nf
.ad
.fi
The input format for the \fBpostmap\fR(1) command is as follows:
.IP "\fIpattern address, address, ...\fR"
When \fIpattern\fR matches a mail address, replace it by the
corresponding \fIaddress\fR.
.IP "blank lines and comments"
Empty lines and whitespace\-only lines are ignored, as
are lines whose first non\-whitespace character is a `#'.
.IP "multi\-line text"
A logical line starts with non\-whitespace text. A line that
starts with whitespace continues a logical line.
.SH "TABLE SEARCH ORDER"
.na
.nf
.ad
.fi
With lookups from indexed files such as DB or DBM, or from networked
tables such as NIS, LDAP or SQL, each \fIuser\fR@\fIdomain\fR
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.
.IP "\fIuser\fR@\fIdomain address, address, ...\fR"
Redirect mail for \fIuser\fR@\fIdomain\fR to \fIaddress\fR.
This form has the highest precedence.
.IP "\fIuser address, address, ...\fR"
Redirect mail for \fIuser\fR@\fIsite\fR to \fIaddress\fR when
\fIsite\fR is equal to $\fBmyorigin\fR, when \fIsite\fR is listed in
$\fBmydestination\fR, or when it is listed in $\fBinet_interfaces\fR
or $\fBproxy_interfaces\fR.
.sp
This functionality overlaps with the functionality of the local
\fIaliases\fR(5) database. The difference is that \fBvirtual\fR(5)
mapping can be applied to non\-local addresses.
.IP "@\fIdomain address, address, ...\fR"
Redirect mail for other users in \fIdomain\fR to \fIaddress\fR.
This form has the lowest precedence.
.sp
Note: @\fIdomain\fR is a wild\-card. With this form, the
Postfix SMTP server accepts
mail for any recipient in \fIdomain\fR, 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.
.sp
To avoid backscatter with mail for a wild\-card domain,
replace the wild\-card mapping with explicit 1:1 mappings,
or add a reject_unverified_recipient restriction for that
domain:

.nf
    smtpd_recipient_restrictions =
        ...
        reject_unauth_destination
        check_recipient_access
            inline:{example.com=reject_unverified_recipient}
    unverified_recipient_reject_code = 550
.fi

In the above example, Postfix may contact a remote server
if the recipient is aliased to a remote address.
.SH "RESULT ADDRESS REWRITING"
.na
.nf
.ad
.fi
The lookup result is subject to address rewriting:
.IP \(bu
When the result has the form @\fIotherdomain\fR, the
result becomes the same \fIuser\fR in \fIotherdomain\fR.
This works only for the first address in a multi\-address
lookup result.
.IP \(bu
When "\fBappend_at_myorigin=yes\fR", append "\fB@$myorigin\fR"
to addresses without "@domain".
.IP \(bu
When "\fBappend_dot_mydomain=yes\fR", append
"\fB.$mydomain\fR" to addresses without ".domain".
.SH "ADDRESS EXTENSION"
.na
.nf
.fi
.ad
When a mail address localpart contains the optional recipient delimiter
(e.g., \fIuser+foo\fR@\fIdomain\fR), the lookup order becomes:
\fIuser+foo\fR@\fIdomain\fR, \fIuser\fR@\fIdomain\fR, \fIuser+foo\fR,
\fIuser\fR, and @\fIdomain\fR.

The \fBpropagate_unmatched_extensions\fR parameter controls whether
an unmatched address extension (\fI+foo\fR) is propagated to the
result of a table lookup.
.SH "VIRTUAL ALIAS DOMAINS"
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.nf
.ad
.fi
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 \fBvirtual\fR(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
\fBaliases\fR(5) and local mailing lists are not visible as
\fIlocalname@virtual\-alias.domain\fR.

Support for a virtual alias domain looks like:

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

Note: some systems use \fBdbm\fR databases instead of \fBhash\fR.
See the output from "\fBpostconf \-m\fR" for available database types.

.nf
/etc/postfix/virtual:
    \fIvirtual\-alias.domain    anything\fR (right\-hand content does not matter)
    \fIpostmaster@virtual\-alias.domain postmaster\fR
    \fIuser1@virtual\-alias.domain      address1\fR
    \fIuser2@virtual\-alias.domain      address2, address3\fR
.fi
.sp
The \fIvirtual\-alias.domain anything\fR entry is required for a
virtual alias domain. \fBWithout this entry, mail is rejected
with "relay access denied", or bounces with
"mail loops back to myself".\fR

Do not specify virtual alias domain names in the \fBmain.cf
mydestination\fR or \fBrelay_domains\fR configuration parameters.

With a virtual alias domain, the Postfix SMTP server
accepts mail for \fIknown\-user@virtual\-alias.domain\fR, and rejects
mail for \fIunknown\-user\fR@\fIvirtual\-alias.domain\fR as undeliverable.

Instead of specifying the virtual alias domain name via
the \fBvirtual_alias_maps\fR table, you may also specify it via
the \fBmain.cf virtual_alias_domains\fR configuration parameter.
This latter parameter uses the same syntax as the \fBmain.cf
mydestination\fR configuration parameter.
.SH "REGULAR EXPRESSION TABLES"
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.nf
.ad
.fi
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 \fBregexp_table\fR(5)
or \fBpcre_table\fR(5).

Each pattern is a regular expression that is applied to the entire
address being looked up. Thus, \fIuser@domain\fR mail addresses are not
broken up into their \fIuser\fR and \fI@domain\fR constituent parts,
nor is \fIuser+foo\fR broken up into \fIuser\fR and \fIfoo\fR.

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 \fB$1\fR, \fB$2\fR and so on.
.SH "TCP-BASED TABLES"
.na
.nf
.ad
.fi
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 \fBtcp_table\fR(5).
This feature is available in Postfix 2.5 and later.

Each lookup operation uses the entire address once.  Thus,
\fIuser@domain\fR mail addresses are not broken up into their
\fIuser\fR and \fI@domain\fR constituent parts, nor is
\fIuser+foo\fR broken up into \fIuser\fR and \fIfoo\fR.

Results are the same as with indexed file lookups.
.SH BUGS
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.fi
The table format does not understand quoting conventions.
.SH "CONFIGURATION PARAMETERS"
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.nf
.ad
.fi
The following \fBmain.cf\fR parameters are especially relevant to
this topic. See the Postfix \fBmain.cf\fR file for syntax details
and for default values. Use the "\fBpostfix reload\fR" command after
a configuration change.
.IP "\fBvirtual_alias_maps ($virtual_maps)\fR"
Optional lookup tables that alias specific mail addresses or domains
to other local or remote addresses.
.IP "\fBvirtual_alias_domains ($virtual_alias_maps)\fR"
Postfix is the final destination for the specified list of virtual
alias domains, that is, domains for which all addresses are aliased
to addresses in other local or remote domains.
.IP "\fBpropagate_unmatched_extensions (canonical, virtual)\fR"
What address lookup tables copy an address extension from the lookup
key to the lookup result.
.PP
Other parameters of interest:
.IP "\fBinet_interfaces (all)\fR"
The network interface addresses that this mail system receives
mail on.
.IP "\fBmydestination ($myhostname, localhost.$mydomain, localhost)\fR"
The list of domains that are delivered via the $local_transport
mail delivery transport.
.IP "\fBmyorigin ($myhostname)\fR"
The domain name that locally\-posted mail appears to come
from, and that locally posted mail is delivered to.
.IP "\fBowner_request_special (yes)\fR"
Enable special treatment for owner\-\fIlistname\fR entries in the
\fBaliases\fR(5) file, and don't split owner\-\fIlistname\fR and
\fIlistname\fR\-request address localparts when the recipient_delimiter
is set to "\-".
.IP "\fBproxy_interfaces (empty)\fR"
The network interface addresses that this mail system receives mail
on by way of a proxy or network address translation unit.
.SH "SEE ALSO"
.na
.nf
cleanup(8), canonicalize and enqueue mail
postmap(1), Postfix lookup table manager
postconf(5), configuration parameters
canonical(5), canonical address mapping
.SH "README FILES"
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.nf
.ad
.fi
Use "\fBpostconf readme_directory\fR" or
"\fBpostconf html_directory\fR" to locate this information.
.na
.nf
ADDRESS_REWRITING_README, address rewriting guide
DATABASE_README, Postfix lookup table overview
VIRTUAL_README, domain hosting guide
.SH "LICENSE"
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.nf
.ad
.fi
The Secure Mailer license must be distributed with this software.
.SH "AUTHOR(S)"
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.nf
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