Postfix Virtual Users

[Lucas Peet]

To any postfix users out there:

I've heard a few things about Postfix and Virtual users / Virtual domains, but have been having a 
hard time finding any solid information on it.

Basically, here is my goal:

I want to be able to add domains, and have each of those domains get their own namespace (so 
bob at domain1.com doesn't conflict with bob at domain2.com, etc...).  I also want these users to not be 
actual users on the system (not listed in /etc/passwd), but to be able to pull their email via pop 
/ imap only.

I know there would need to be some way to authenticate the users via pop/imap besides /etc/passwd 
(mySQL maybe?).

Where would the virtual user's incoming email be stored, since there wouldn't be home directories 
for Maildir/ to go in?

Is this type of configuration even possible?  I'm using RedHat 7.2, with Postfix and courier-imap.

Any help would be much appreciated!

-Lucas