SpamAssassin on its own can detect a high proportion of spam. By using network tests, spam detection can be further improved. SpamAssassin includes support for Realtime BlockLists (RBLs) and Spam URI Realtime BlockLists (SURBLs). All these external services are easy to integrate into SpamAssassin.
The effectiveness of network tests varies from a 60% detection rate upwards. By using them in conjunction with SpamAssassin, spam detection rates are much higher, typically over 95%! However, network tests slow down spam detection. This means that the SpamAssassin processes will take longer to complete and will increase the memory usage of the email server.
This chapter describes the support SpamAssassin has for RBLs and SURBLs, and focuses on three external services:
Vipul's Razor
Pyzor
The Distributed Checksum Clearinghouse (DCC)
RBLs are blocklists of known sources of spam. By default, SpamAssassin uses a number of RBLs to check the source of the email.
A SURBL is a blocklist...
