Rspamd - Fast, free and open-source spam filtering system
Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules including regular expressions, statistical analysis and custom services such as URL black lists. It supports Regular expressions filtering, SPF, DKIM, DNS black list, URL black lists, Fuzzy hashes etc.
According to this spam score and the user's settings, Rspamd recommends an action for the MTA to apply to the message, for example, to pass, reject or add a header. Rspamd is designed to process hundreds of messages per second simultaneously, and provides a number of useful features.