Enable sieve body MTA option

Sieve language extension MTA options:  (0-2)
(New in Messaging Server 7.0u2) This option controls whether Sieve filters may use the  body extension. The default value is 0, meaning that body is not available. A value of 1 allows body to be used in any Sieve script. A value of 2 allows body to be used in system-level Sieves only.

See also:
 * Sieve body extension
 * Sieve language extension MTA options