http://www.rfc-editor.org/rfc/rfc4315.txt
RFC 4315: Internet Message Access Protocol (IMAP) - UIDPLUS extension, M. Crispin2005-12-01T23:00:00-00:00The UIDPLUS extension of the Internet Message Access Protocol (IMAP) provides a set of features intended to reduce the amount of time and resources used by some client operations. The features in UIDPLUS are primarily intended for disconnected-use clients. [STANDARDS-TRACK]