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 has a number of features available.