Policyd is an anti-spam plugin for Postfix (written in C) that does Greylisting, Sender-(envelope, SASL or host / ip)-based throttling (on messages and/or volume per defined time unit), Recipient rate limiting, Spamtrap monitoring / blacklisting, HELO aut
Fighting spam must be a complex solution, and here is several examples of how to do it quite efficiently using Postfix, ClamAV with clamstmpd, dkfilter DomainKeys, DNSBL, Gld greylisting, SPF