Sieve ihave extension

As of Messaging Server 7.0, the MTA supports the Sieve  extension described in RFC 5463 (Sieve Email Filtering: Ihave Extension);  the capability name is " ". This includes the " " test and the " " control structure.

The  test takes as argument a list of capability names and returns   if all the listed capabilities are available to the Sieve script. Thus this permits a Sieve script to be coded in such a way as to be flexible regarding what extensions it attempts to use, and also potentially to be portable (run in different environments). In particular, when a capability&#x27;s availability has been confirmed via a successful   test, then that extension becomes available throughout the entire Sieve script, as if it had been listed in a   action. The  control structure may be used when it is desired to exit with a runtime error if an   test fails (a capability is not available).

See also:
 * Sieve supported extensions
 * Sieve filters