Actually, I've two server on my place.
One SME for the Internet Gateway/PHP/MySQL and One Win2K just for the Exchange Server and Domain account.
Workstation are Win2K/WinXP with outlook.
My Dream, put the Win2K server out of my place.
But I can do that without a good replacement of Exchange Server.
I've try many Linux Mail Server solution, the better solution (more complete) I've try is Samsung Contact, but it's not for Free
SME must find a solution to let the choice to the users :
Single Imap connection without pay of outlook connector.
Or Full Feature Outlook with pay for oultook connector
The Samba 3.0 is released with active directory support.
It's the first way for a good implementation of a real workgroup.
http://www.samsungcontact.com/en/downloads/?si=5b0ebe9f137a6d738f7876f20f322