A New Internet-Draft is available from the on-line Internet-Drafts directories. This draft is a work item of the Internet Message Access Protocol Extension Working Group of the IETF.
This document describes the base-level server-based sorting and threading extensions to the IMAP protocol. These extensions provide substantial performance improvements for IMAP clients which offer sorted and threaded views.
http://www.ietf.org/internet-drafts/draft-ietf-imapext-sort-14.txt