A New Internet-Draft is available from the on-line Internet-Drafts directories. This draft is a work item of the Enhancements to Internet email to support diverse service environments Working Group of the IETF.
The CATENATE extension to the Internet Message Access Protocol (IMAP) allows clients to create messages on the IMAP server which may contain a combination of new data along with parts of (or entire) messages already on the server. Using this extension, the client can catenate parts of an already existing message on to a new message without having to first download the data and then upload it back to the server.
http://www.ietf.org/internet-drafts/draft-ietf-lemonade-catenate-00.txt