Why dont improve on IMAP with extensions, I can't see how the "extending IMAP only makes it worse" argument hold. How would adding an addition protocol (JMAP) t

Why dont improve on IMAP with extensions, I can't see how the "extending IMAP only makes it worse" argument hold. How would adding an addition protocol (JMAP) to a buggy client make the situation any better? I can see how it's easier for fastmail as a company to try to get its changes out by making another protocol, but would we not benefit better by trying to improve on IMAP? it's very unlikely this will ever replace IMAP and SMTPS from history internet always try to iterate and improve not replace standards completely? There is great effort to improve on SMTP and encryption lately, what can we learn from that?