To revisit what I said in the first post in our Postfix series, a virtual setup is one in which email accounts are independent of system accounts. We therefore have to tell Postfix what accounts we have on any given domain, where to put email for an account etc. unlike local delivery where users are given by the system and delivery is by default to a file in /var/mail. In order to create this kind of setup we will have to jettison most of the settings we have worked on so far. On the plus side it will still feel very familiar as settings are often in parallel. And you’ll understand how to properly distinguish between the two kinds of setup.
From the outside there will be no discernible difference. Our Postfix server will accept mail for users on legitimate domains and reject mail for all other destination.