What are some alternatives?
EuropeanMX - Protects your company by blocking spam and virus before they reach your network.
Scrollout F1 - Scrollout is a free and easy to use anti-spam email gateway designed for Linux & Windows administrators without advanced email security experience.
Hornetsecurity - Hornetsecurity offers you comprehensive, integrated managed e-mail security services.
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.
Symantec Email Security.cloud - Symantec Email Security.cloud provides always-on, inbound and outbound email security against malware, targeted attacks, and advanced threats
Mailwasher - Over 8 million people use MailWasher as their spam filter