What are some alternatives?
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.
Mailwasher - Over 8 million people use MailWasher as their spam filter
Spamihilator - The free Anti-Spam-Filter Spamihilator removes more than 98% of spam mails before they even get into your inbox.
Scrollout F1 - Scrollout is a free and easy to use anti-spam email gateway designed for Linux & Windows administrators without advanced email security experience.
Spam Reader - Spam Reader is a free anti-spam add-on for Microsoft Outlook.
SPAMfighter - SPAMfighter and Microsoft have built the strongest and most effective anti spam filter for Outlook, Windows Live Mail, Outlook Express & Thunderbird