Tough order to fill. I looked and looked and found nothing for Windows. Linux is a different story. There's a few options there. I wanted to stay with Windows, so I ponied up the cash for MailEnable Pro.
If you decide to go the Linux route, check out
SME Server. It pretty much sets itself up and it has a webserver, mail server, webmail, IMAP, firewall, and Samba. And it's free.