I’m currently using the free hMailServer for SMTP, POP3, and IMAP. It has been pretty solid in the couple years that I’ve been using it. I’ve run it on Windows 2003 R2 and Windows 2008 Standard and Enterprise. I’m using SquirrelMail for webmail. This is PHP, but it wasn’t that hard to setup. This is free as well.
The best commercial experience that I had with a non-Exchange server was MDaemon from Alt-N Technologies. It has the best OWA like UI, and it has a connector for Outlook, so that it thinks it is an Exchange server. The price for this server is not as much as others, but still too much for me.
There are several other email servers:
Open Source/Free
- Zimbra – http://www.zimbra.com/
- MailEnable Standard – http://www.mailenable.com/
Commercial
- Kerio MailServer – http://www.kerio.com/mailserver
- MailEnable Professional or above – http://www.mailenable.com/
- Softtalk Mail Server (Workgroup Mail Server) – http://www.softalkltd.com/products/workgroupmail/
There are many more servers out there. The ones I listed here are the ones I had tried at one point in the past.