Abstract from the RFC text:
On email systems that allow for 'subaddressing' or 'detailed addressing' (e.g., "ken+sieve@example.org"), it is sometimes desirable to make comparisons against these sub-parts of addresses. This document defines an extension to the Sieve Email Filtering Language that allows users to compare against the user and detail sub-parts of an address.
Notes: None
There is 1 reported erratum for RFC 5233 (as of 2008-08-25).
Used in the following classes: