razor - 1:2.85-4.2+b5 main

Vipul's Razor is a distributed, collaborative, spam detection and
filtering network. Razor establishes a distributed and constantly updating
catalogue of spam in propagation. This catalogue is used by clients to
filter out known spam. On receiving a spam, a Razor Reporting Agent (run
by an end-user or a troll box) calculates and submits a 20-character unique
identification of the spam (a SHA Digest) to its closest Razor
Catalogue Server. The Catalogue Server echos this signature to other
trusted servers after storing it in its database. Prior to manual
processing or transport-level reception, Razor Filtering Agents (end-users
and MTAs) check their incoming mail against a Catalogue Server and filter
out or deny transport in case of a signature match. Catalogued spam, once
identified and reported by a Reporting Agent, can be blocked out by the
rest of the Filtering Agents on the network.