This chapter has only scratched the surface of SpamAssassin's capabilities. If spam is a problem for an organization, SpamAssassin will reward further study. Some of the other features that it contains are as follows:
Network tests: SpamAssassin can integrate with Open Relay Databases. (The 3.x distribution contains tests for over 30 databases, although not all of them are enabled by default.) Open Relay tests do not require a fast machine or lots of RAM, and so are relatively cheap tests to use. They have a fairly successful detection rate.
External content databases: SpamAssassin can integrate with external content databases. These work in a participating network. All the participants send details of all the e-mails they receive to central servers. If the e-mails have been sent many times before, the e-mail is probably a spam that has been sent to many users. The services are designed so that no confidential data is sent.
Whitelist and blacklist: SpamAssassin...