While IMAP is very much a live protocol, I do not know that any of the currently active core developers know much about it. Imaplib is based on the obsolete RFC2060 of Dev 1996, superseded by 3501 in March 2003, with 6 later updates. (I just found all this out to respond here.)

It is written in Python. If you take a look at the code, you will see that 7 people have contributed additions after the initial writing (and others may have contributed unlisted patches). Feel free to submit another by yourself.