http://www.rfc-editor.org/rfc/rfc5464.txt
RFC 5464: The IMAP METADATA Extension, C. Daboo2009-02-01T23:00:00-00:00The METADATA extension to the Internet Message Access Protocol permits clients and servers to maintain "annotations" or "metadata" on IMAP servers. It is possible to have annotations on a per-mailbox basis or on the server as a whole. For example, this would allow comments about the purpose of a particular mailbox to be "attached" to that mailbox, or a "message of the day" containing server status information to be made available to anyone logging in to the server. [STANDARDS-TRACK]