Well.. any imap service is not
related to domains.|
When it comes to users, it's a matter of what kind of authentication you want to use, and
what backend you care the most for.
It all depends on how big the volume is on domains and e-mail, that was my biggest concern.
You can stick to creating users, and letting pam taking care of everything.
Radius is an option, LDAP could suite you just fine.. I chose for the relational database
setup for a small vhosting company.
I'm quite happy with the postfix-courier(imap/pop3)-mysql-backend option I choose.
It's a bit of a hassle to get all sorted, but high5 has a couple of interfaces that makes it
a lot easier to maintain the enviroment. It's nothing fancy, but it does the trick.
If you need to expand it's quite easy to setup a load balancing act based on this setup.