[Exim] Virtual Host woes

Hi,

I've been searching for some virtual-hosting solutions. Something where I
don't have to worry about mapping virtual users to local users.

I've seen proprietary setups for users like:
/home/fubar/etc/passwd
All the uids are set to the same thing as fubar's uid (an actual system
account).

Then they use a proprietary pop3/smtp server to retreive email (by using a
full email address for logins).

Any idea on an equivalent?

Just thought I'd search for what some people use for a solution.

Thanks,
James Harr
PS - I don't care whether it is a blackbox approach or not, I just want
something that works and isn't a half-assed setup.