Address masquerading is a method to hide all hosts below 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.
Address masquerading is disabled by default. To enable, specify one or more
domain names separated by whitespace or commas. For example: $mydomain
; in this example, addresses of the form user@host.$mydomain would be
rewritten to user@$mydomain.