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. Each message is analysed by Rspamd and given a spam score.
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. More Info »
You can watch the following introduction video from FOSDEM-2016 where I describe the main features of Rspamd and explain why Rspamd is so fast.
Rspamd is packaged for the major Linux distributions, and is also available via FreeBSD ports, NetBSD pkgsrc and OpenBSD ports.