SIEVE Email Filtering: Spamtest and Virustest Extensions
The SIEVE email filtering language "spamtest", "spamtestplus" and "virustest" extensions permit users to use simple, portable commands for spam and virus tests on email messages. Each extension provides a new test using matches against numeric "scores". It is the responsibility of the underlying SIEVE implementation to do the actual checks that result in proper input to the tests.