Accepting mail for multiple domains where every user can receive mail for every domain is the simplest configuration of virtual domains. Simply add your virtual domains to the mydestination parameter. Create user accounts as you normally would, and they can start receiving mail addressed to any of the domains. This technique uses the local delivery agent, providing all of the same features as your normal canonical domain hosting. Users can create their own .forward files, and local aliases are available. On a system whose canonical name is oreillynet.com, hosting two virtual domains, ora.com and oreilly.com, the mydomain parameter is set as if oreillynet.com were the only domain, and mydestination is set as follows:
mydomain = oreillynet.com mydestination = $myhostname, $mydomain, ora.com, oreilly.com
Make sure you reload Postfix after making changes. Users can now receive mail at any of the domains you listed in mydestination:
# postfix reload
Messages addressed to either email@example.com or firstname.lastname@example.org all go to the same local user account.