I'm currently running MailEnable as my email server, it's ok but lacking. I'm looking for a better alternative and am wondering about Open Source. I'm a huge fan of the Smarter Mail, and will pay if it's the best I can get... But I have been learning that there is some good stuff out there in the Open Source community (IE: I've started using PFSense and I love it).
OS doesn't matter, though I would prefer Windows.
Does anyone have any suggestions?