[Postfix] Add support for masquerade_domains
The postfix option masquerade_domains is a handy feature:
Address masquerading is a method to hide hosts inside a domain behind their mail gateway, and to make it appear as if the mail comes from the gateway itself, instead of from individual machines.
Example:
/etc/postfix/main.cf:
masquerade_domains = foo.example.com example.com
strips "any.thing.foo.example.com" to "foo.example.com", but strips "any.thing.else.example.com" to "example.com".
Full text here: http://www.postfix.org/ADDRESS_REWRITING_README.html#masquerade