mxORB 

mxORB is a server-side spam filter that consistently blocks over 98% of unsolicited commercial email (also known as spam) at a fraction of the cost of other filtering solutions.
exchange 2000 spam filter exchange 2003 spam filter exchange spam filter exchange iis smtp uce unsolicited commercial email spam filter open relay blacklist event

602LAN SUITE 

Secure mail server with anti-virus & anti-spam, built-in firewall with NAT and real-time web content filter proxy for controlled Internet sharing. Access your e-mail anywhere using the included web mail client. The 5 user version is FREE.
content filter free secure e-mail mail web fax server anti-virus anti-spam spam nat proxy protection

ORF Enterprise Edition 

ORF Enterprise Edition is an enterprise-level anti-spam solution that helps you to block spam before it reaches your network. ORF uses a combination of anti-spam technologies to stop the spam on SMTP protocol level.
exchange spam filter open relay rbl email filter anti-spam