Anti-Spam SMTP Proxy Server implements multiple spam filters
Universal server
Mailing List Manager - Web-based, Self-Hosted, Feature-Rich
Anti Spam SMTP Gateway
Process messages held by Mailman for approval
Zentyal is a Linux Small Business Server
Full SMTP/Mail server Appliance in 5 minutes
Command line utility for administering Sympa mailing lists.
Open Source Anti-Spam and Anti-Virus Gateway
AV/content filter for Qmail