email on linux question...

I'm trying to find a email configuration on linux that has the following
proterties...

1) virtual users. IE: [email]lbaker@domain1.com[/email] is a different user than
[email]lbaker@domain2.com[/email] and lbaker does not have to be a linux user at all.

2) SMTP authentication is supported.

3) POP3 and IMAP are both supported.

Essentially, I want email completely divorced from the os users and I
want real virtual users per domain.

I'm currently running sendmail and dovecote and I have not yet found a
setting that allows this.

Which apps / configuration options will do this, if any at all?

Thanks for the assistance.

Lyle Baker