# phpman > man > virtual(5) [VIRTUAL(5)](https://www.chedong.com/phpMan.php/man/VIRTUAL/5/markdown) File Formats Manual [VIRTUAL(5)](https://www.chedong.com/phpMan.php/man/VIRTUAL/5/markdown) ## 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)](https://www.chedong.com/phpMan.php/man/virtual/5/markdown) alias table rewrites recipient addresses for all local, all virtual, and all remote mail destinations. This is unlike the [**aliases**(5)](https://www.chedong.com/phpMan.php/man/aliases/5/markdown) table which is used only for [**local**(8)](https://www.chedong.com/phpMan.php/man/local/8/markdown) delivery. Virtual aliasing is recursive, and is implemented by the Postfix [**cleanup**(8)](https://www.chedong.com/phpMan.php/man/cleanup/8/markdown) 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)](https://www.chedong.com/phpMan.php/man/virtual/8/markdown) mail delivery agent. With virtual mailbox do‐ mains, 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)](https://www.chedong.com/phpMan.php/man/canonical/5/markdown) mapping to rewrite header and envelope addresses in general. Normally, the [**virtual**(5)](https://www.chedong.com/phpMan.php/man/virtual/5/markdown) alias table is specified as a text file that serves as input to the [**postmap**(1)](https://www.chedong.com/phpMan.php/man/postmap/1/markdown) 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 TA‐ BLES" 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)](https://www.chedong.com/phpMan.php/man/postmap/1/markdown) 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-white‐ space 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 pat‐ tern, 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 $**proxy**___**inter**‐‐ **faces**. This functionality overlaps with functionality of the local [_aliases_(5)](https://www.chedong.com/phpMan.php/man/aliases/5/markdown) database. The difference is that [**virtual**(5)](https://www.chedong.com/phpMan.php/man/virtual/5/markdown) mapping can be applied to non-local addresses. @_domain_ _address,_ _address,_ _..._ Redirect mail for other users in _domain_ to _address_. This form has the lowest prece‐ dence. Note: @_domain_ is a wild-card. With this form, the Postfix SMTP server accepts mail for any recipient in _domain_, regardless of whether that recipient exists. This may turn your mail system into a backscatter source: Postfix first accepts mail for non-exis‐ tent recipients and then tries to return that mail as "undeliverable" to the often forged sender address. To avoid backscatter with mail for a wild-card domain, replace the wild-card mapping with explicit 1:1 mappings, or add a reject_unverified_recipient restriction for that domain: smtpd_recipient_restrictions = ... reject_unauth_destination check_recipient_access inline:{example.com=reject_unverified_recipient} unverified_recipient_reject_code = 550 In the above example, Postfix may contact a remote server if the recipient is aliased to a remote address. ## RESULT ADDRESS REWRITING The lookup result is subject to address rewriting: • When the result has the form @_otherdomain_, the result becomes the same _user_ in _other__‐ _domain_. This works only for the first address in a multi-address lookup result. • When "**append**___**at**___**myorigin=yes**", append "**@$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_@_do__‐ _main_), 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 imple‐ mented with the Postfix [**virtual**(8)](https://www.chedong.com/phpMan.php/man/virtual/8/markdown) 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)](https://www.chedong.com/phpMan.php/man/aliases/5/markdown) 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** **my**‐‐ ### self". Do not specify virtual alias domain names in the **main.cf** **mydestination** or **relay**___**domains** con‐ figuration parameters. With a virtual alias domain, the Postfix SMTP server accepts mail for _known-user@vir__‐ _tual-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 **reg**‐‐ **exp**___**[table**(5)](https://www.chedong.com/phpMan.php/man/table/5/markdown) or **pcre**___**[table**(5)](https://www.chedong.com/phpMan.php/man/table/5/markdown). 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 parenthe‐ sized substrings from the pattern can be interpolated as **$1**, **$2** and so on. ## TCP-BASED TABLES This section describes how the table lookups change when lookups are directed to a TCP-based server. For a description of the TCP client/server lookup protocol, see **tcp**___**[table**(5)](https://www.chedong.com/phpMan.php/man/table/5/markdown). This feature is not available up to and including Postfix version 2.4. Each lookup operation uses the entire address once. Thus, _user@domain_ mail addresses are not broken up into their _user_ and _@domain_ constituent parts, nor is _user+foo_ broken up into _user_ and _foo_. Results are the same as with indexed file lookups. ## BUGS The table format does not understand quoting conventions. ## CONFIGURATION PARAMETERS The following **main.cf** parameters are especially relevant to this topic. See the Postfix **main.cf** file for syntax details and for default values. Use the "**postfix** **reload**" command af‐ ter a configuration change. **virtual**___**alias**___**maps** **($virtual**___**maps)** Optional lookup tables that alias specific mail addresses or domains to other local or remote address. **virtual**___**alias**___**domains** **($virtual**___**alias**___**maps)** Postfix is final destination for the specified list of virtual alias domains, that is, domains for which all addresses are aliased to addresses in other local or remote do‐ mains. **propagate**___**unmatched**___**extensions** **(canonical,** **virtual)** What address lookup tables copy an address extension from the lookup key to the lookup result. Other parameters of interest: **inet**___**interfaces** **(all)** The network interface addresses that this mail system receives mail on. ### mydestination ($myhostname, localhost.$mydomain, localhost) The list of domains that are delivered via the $local_transport mail delivery trans‐ port. ### myorigin ($myhostname) The domain name that locally-posted mail appears to come from, and that locally posted mail is delivered to. **owner**___**request**___**special** **(yes)** Enable special treatment for owner-_listname_ entries in the [**aliases**(5)](https://www.chedong.com/phpMan.php/man/aliases/5/markdown) file, and don't split owner-_listname_ and _listname_-request address localparts when the recipient_delim‐ iter is set to "-". **proxy**___**interfaces** **(empty)** The network interface addresses that this mail system receives mail on by way of a proxy or network address translation unit. ## SEE ALSO [cleanup(8)](https://www.chedong.com/phpMan.php/man/cleanup/8/markdown), canonicalize and enqueue mail [postmap(1)](https://www.chedong.com/phpMan.php/man/postmap/1/markdown), Postfix lookup table manager [postconf(5)](https://www.chedong.com/phpMan.php/man/postconf/5/markdown), configuration parameters [canonical(5)](https://www.chedong.com/phpMan.php/man/canonical/5/markdown), 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)](https://www.chedong.com/phpMan.php/man/VIRTUAL/5/markdown)