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Extensions

This section summarizes the GNU extensions to the sieve language

1. Handling of the require statement.
   • According to the RFC an error must occur if a require appears after a command other than require. The GNU sieve library allows interspersing the require and other statements. The only requirement is that require must occur before a statement that is using the required capability (see Require Statement).
   • Prefixing the required capability with "test" requires the use of an extension test.
2. header test

   The header takes an optional argument :mime, meaning to scan the headers from each part of a multipart message.

3. size test

   The size test allows to omit the optional argument (:over|:under). In this case exact equality is assumed.

4. envelope test

   The only value that can be meaningfully used as the first required argument of an envelope test is from. This limitation may disappear from the subsequent releases.

5. Match type optional argument.

   Along with the usual :is, :matches and contains matching type, GNU sieve library understands :regex type. This matching type toggles POSIX Extended Regular Expression matching.