5.8 GNU Extensions

This section summarizes the GNU extensions to the sieve language

1. Multiline strings syntax

   GNU libsieve understands the following multiline string syntax:

   text:[-][delimiter] .... delimiter

   The meaning of optional flags is the same as in shell "here document" construct: the dash strips all leading tab characters from the string body, thus allowing it to be indented in a natural fashion; delimiter introduces the new end-of-text delimiter instead of the default dot. If delimiter starts with a backslash, no preprocessing will be performed within a string.

2. 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 section 5.4 Require Statement).

   • Prefixing the required capability with "test" requires the use of an extension test.

3. header test

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

4. size test

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

5. 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.

6. 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.