Wikipedia
Policyd-weight
policyd-weight is a mail filter for the Postfix mail transfer agent (MTA) written in Perl, by Robert Felber. It allows postfix to evaluate mail envelope information and to score mail against several DNS-based Blackhole Lists ( DNSBL) before the mail is queued. The final score will determine whether a mail is rejected or accepted, in which case it is usually then subject to more resource intensive checks by a virus scanner and spam filter.