[imp] IMP and Domains?

[Devin Atencio]

I was curious how the correct way to use Horde::IMP to make virtual domains
fly? I have like 10 domains in my servers.php file. Previously I modified
the imp/redirect.php and added some special code to allow for the username
to be entered as: username@domain.com, then the redirect would re-assign
the $HTTP_POST_VARS[imapuser] and $HTTP_POST_VARS[server] 
accordingly by parsing out the @ sign, but this no longer works since
I downloaded the 3.1.1 version of IMP. 

How do I get it so that when username: devin logs in it uses domain 
phpcodeguru.com, and if a user name Aether logs in it uses domain
djaether.com, etc?

Any help would be greatly appreciated.