It is very common these days for a single system to host
many domains. For instance, http://oreillynet.com and http://onlamp.com might run on a single host, but act as
if they were two totally different hosts. A system usually has a
canonical domain, which is considered its usual or common domain
name. Additional domains are configured as
virtual domains. Each virtual domain can host services such as web
sites and email as if it were the only domain on a server. This chapter
explains several different mechanisms for hosting multiple domains. The
techniques are explained separately, but it is possible to mix techniques
if you must handle different domains in different ways.
To determine which technique or techniques you need, you must decide how Postfix should deliver messages for virtual domains. There are two important considerations that influence how you should configure Postfix for hosting multiple domains:
Should your domains have separate namespaces? For example, should mail for the two addresses email@example.com and firstname.lastname@example.org go to the same mailbox or separate ones? We’ll refer to the same mailbox scenario as shared domains, and the other as separate domains.
Does every user require a system account? We’ll make the distinction between system accounts that are real Unix accounts on your system and virtual accounts. With virtual accounts, users can have mailboxes on your server, but don’t otherwise log in to the system and don’t require ...