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.
SpamTitan - SpamTitan is an anti-spam email solution specifically developed to meet the demands of modern business. Delivering a spam detection rate over 99.9%
SpamAssassin - Use this program to "Unspam" your mailbox(es).