This document outlines the setup of a typical Sendmail -> DSPAM -> Procmail system. If you don't use Procmail, then substitute your LDA where applicable.
DSPAM is a scalable and open-source content-based spam filter designed for multi-user enterprise systems. On a properly configured system, many users experience results between 99.5% - 99.95%, or one error for every 200 to 2000 messages. DSPAM supports ma