IMail GUI equivalent for Linux?

[Steen Suder, privat]

In the process of setting a little web & mail-hotel up, I've stumbled 
over a user-suggestion that calls for a webinterface for handling 
emailaddresses, forwards, spamfiltering and so on that is similar to the 
UI of the IMail Server (http://www.ipswitch.com/Products/IMail_Server/).

The MTA will probably be either Exim or Postfix as I've no interest in 
Qmail. Local delivery is handled by what is necessary and reliable 
(Courier, Cyrus, whatever).

Users email access is POP3 and, secondarily, IMAP (for a few VIP-customers).
Any suggestions are welcome (also non-free and commercial ones).
--
Mvh. / Best regards,
Steen Suder             <http://www.suder.dk/>
ICQ UIN                 4133803