POP3 Mail Server Recommendation Please

[JoshWithrow]

Our company is in need of a good web based mail solution. We currently use i-Mail, but are very unhappy with it's lack of features, both client and server applications.

Please drop me any recommendations. We're searching for soemething that is/has:

1. Intuitive
2. Feature Rich: Mail Forwarding, vac message, auto-responders, ability to manage folders, etc.
3. works in a win32/server environment
4. easily installed/upgraded
5. has wide support for add-ons
6. has or can handle SPAM FILTERS!!!
7. good working advanced processing rules.

Thanks!!!