What are some alternatives?
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.
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.
Spamihilator - The free Anti-Spam-Filter Spamihilator removes more than 98% of spam mails before they even get into your inbox.
Proxmox Mail Gateway - Protect mail server against spam, viruses and malware with Proxmox Mail Gateway security for businesses, government, education and non-profit organizations.
Spamfence.net - Professional e-mail security free for private use: With Spamfence.