Exchange-level Mail Server Software

SmarterMail delivers Exchange-level email server software and instant messaging for a fraction of the cost. With lower hardware requirements, superior stability and reduced maintenance costs, SmarterMail has significantly lower TCO and is the best-in-class Microsoft Exchange alternative for businesses and hosting companies.

https://www.smartertools.com/smartermail/mail-server-software.aspx

Available from Mail's Best Friend

MBF Recommended Anti-Spam Settings for Smarter Mail