Supporting Virtual Domains
Postfix natively supports virtual domain hosting styles, with two slightly different behaviors. The Postfix-style virtual domain has a unique namespace, meaning that you can have a email@example.com, and a firstname.lastname@example.org. In Postfix-style virtual hosting local alias maps and local user accounts are not visible in the virtual domain name space. Postfix will also reject unknown user addresses for Postfix-style virtual domains.
Sendmail-style virtual domains expose local aliases, mailing lists, and local account names to virtual domains. The obvious downside to this is that if you have a sales alias defined for your normal non-virtual domain, it will be exposed as email@example.com, firstname.lastname@example.org, etc. if no sales address is defined in either of those virtual domains. That behavior is probably not what you intended.
To use Postfix-style virtual hosting just add the virtual_map entries defining the virtual domain like so:
/etc/postfix/main.cf: virtual_maps = hash:/etc/postfix/virtual_vdomain1-com hash:/etc/postfix/virtual_vdomain2-com
Then, create each virtual domain map. For Postfix-style maps you must list the virtual domain on the first line. It actually does not matter what is on the right side of the virtual domain on the first line, so the domain name is duplicated just out of habit. Then, you can list individual addresses and aliases.
/etc/postfix/virtual_vdomain1-com: vdomain1.com vdomain1.com email@example.com address1 firstname.lastname@example.org address1 email@example.com address2, address3 /etc/postfix/virtual_vdomain2-com: vdomain2.com vdomain2.com firstname.lastname@example.org address11 email@example.com address11 firstname.lastname@example.org address12, address13
After creating the maps, remember to convert them to database lookup tables using the postmap command.
Sendmail-style virtual domains require the domain to be listed in the mydestinations parameter in main.cf, and should not be listed in the virtual map.
/etc/postfix/main.cf: mydestination = $myhostname, localhost.$mydomain, $mydomain vdomain1.com vdomain2.com virtual_maps = hash:/etc/postfix/virtual_vdomain1-com hash:/etc/postfix/virtual_vdomain2-com
The virtual maps are virtually identical, except the domain itself is not listed:
/etc/postfix/virtual_vdomain1-com: email@example.com address1 firstname.lastname@example.org address1 email@example.com address2, address3 /etc/postfix/virtual_vdomain2-com: firstname.lastname@example.org address11 email@example.com address11 firstname.lastname@example.org address12, address13
Each map must be converted from a text file to a database lookup table using the postmap command.
Both the Postfix-style and Sendmail-style virtual domain handling only rewrites the recipient address, not the entire message header. Message header rewriting has two components: domain masquerading and canonical maps.
Domain masquerading is used to remove (and thus masquerade) subdomains such as east.domain.com. When an email addressed from email@example.com leaves the mail server, the email headers get rewritten as firstname.lastname@example.org. To enable domain masquerading list, each domain to be masqueraded in the masquerade_domains parameter.
masquerade_domains = domain.com
Address rewriting, in the form of login to First.Last, can be enabled through the use of canonical maps. Canonical maps essentially provide reverse-map functionality.
canonical_maps = hash:/etc/postfix/canonical_vdomain1-com
The contents of the canonical map file can be any of the following:
/etc/postfix/canonical_vdomain1-com maryjo mary.jo.bobbins dude mr.big.vip mr.big.vip vice.president vice.president mary.jo.bobbins ceo ricky.rat l33t-warez software.development help email@example.com
Canonical address mapping is recursive, so when Mary Jo is promoted to CEO, only the vice.president and ceo mappings would need to be changed. Canonical address maps should not be confused with local aliases. Canonical address maps rewrite the addresses in both the message headers, and the message envelope.