The SEARCH=INTHREAD extension extends the IMAP SEARCH command to operate on threads as well as individual messages. Other commands which search are implicitly extended. This allows clients to perform searches such as "find all threads that mention schemata", rather than just "find all single messages that mention schemata". The THREAD=REFS extension provides a threading algorithm using (almost) only the References header field for use with the IMAP THREAD command. 1.