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SpamAssassin by Alan Schwartz

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Chapter 3. SpamAssassin Rules

SpamAssassin performs its spam-checking by applying a series of tests to an email message. Most tests examine the message headers or body for patterns that are suggestive of spam; others perform Internet lookups against network-based blacklists of IP addresses or checksums of spam messages. Each positive test yields a score, and the sum of the scores is the total spam score of the message.

This chapter describes the SpamAssassin pattern-based and network-based tests: how they are written and scored, and how you can modify the score of a built-in test or write your own custom tests. This chapter also covers whitelist and blacklist rules, which can override SpamAssassin’s usual determination of whether or not a message is spam.

The tests described in this chapter are all static tests—they don’t change over time as SpamAssassin analyzes messages. Chapter 4 explains learning tests, which use information from messages seen in the past to improve decisions in the future.

The Anatomy of a Test

Most SpamAssassin tests consist of the same basic components:

  • A test name, consisting of up to 22 uppercase letters, numbers, or underscores. Names that begin T_ refer to rules in testing.

  • A more verbose description of the test, which is used in the reports generated by SpamAssassin. Typically, descriptions are up to 50 characters long.

  • An indication of where to look. Tests can be applied to the message headers only, the message body only, uniform resource identifiers ...

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