spasm is a highly configurable, highly extensible anti-spam filter written for the sendmail milter API. Its features include:

• Command line and web-based filter/blacklist/whitelist editors
• Logging of blocked spam
• Selectable tagging/quarantining/rejecting for each filter
• Fully virtualised -- supports individual filters, whitelists, and blacklists for any number of virtual domain email addresses, as well as per-domain default settings.
• Whitelist by envelope sender (exact match), server IP address (substring/CIDR), or server hostname (substring).
• Over two dozen blacklist filters to choose from, with an easily extensible framework to add new filters.
• Filters include: local blacklist, rDNS verification, HELO/EHLO verification, envelope sender address verification; DNS blacklists include ordb.org, *.rfc-ignorant.org, and *.blackholes.us.
• Optional content filters: Anti-Virus and SpamAssassin support
• Supports "whitelist-only" mode, rejecting all mail that isn't whitelisted.
• Supports auto-blacklisting of IP addresses based on a maximum threshold of unknown recipient addresses.
• Supports auto-blacklisting of IP addresses based on spamtrap recipient addresses.
• Requires Berkeley DB4