http://www.rfc-editor.org/rfc/rfc2195.txt
RFC 2195: IMAP/POP AUTHorize Extension for Simple Challenge/Response, J. Klensin, R. Catoe, P. Krumviede1997-09-01T23:00:00-00:00This specification provides a simple challenge-response authentication protocol that is suitable for use with IMAP4. [STANDARDS-TRACK]