IETF RFC 5232 PDF

Recent discussions have shown that it is desirable to set different IMAP (RFC 3501) flags on message delivery. This can be done, for example, by a Sieve interpreter that works as a part of a Mail Delivery Agent.

This document describes an extension to the Sieve mail filtering language for setting IMAP flags. The extension allows setting of both IMAP system flags and IMAP keywords.