From LQWiki

The virtual domain support in Postfix is actually quite robust. There are different ways you host virtual domains with Postfix.

• Canonical versus hosted versus other domains

• Local files versus network databases
  • Shared domains, UNIX system accounts
  • Postfix virtual ALIAS example: separate domains, UNIX system accounts
  • Postfix virtual MAILBOX example: separate domains, non-UNIX accounts
  • Non-Postfix mailbox store: separate domains, non-UNIX accounts
  • Mail forwarding domains
  • Mailing lists
  • Autoreplies