Is there any news re JMAP? It’s a nice idea but the goal of finalizing end of 2020 did not work out at all.
The last thing on the JMAP news feed is almost two years ago, announcing Cyrus now supports it. Dovecot doesn’t and Thunderbird doesn’t. There are at least some folks slowly working on Thunderbird but I’ve not seen anything from Dovecot for a few years. It looks as if the attitude from Thunderbird is roughly ‘this is cool, we should support it as soon as Dovecot does!’ and the attitude from Dovecot is ‘this looks interesting, we should support it as soon as Thunderbird does’.
At the moment, it’s basically a Fastmail-only protocol. That’s a shame because it does look like a much better protocol than the combination of SMTP + IMAP + CalDAV + CardDAV + ManageSieve that you need to provide a MAPI/RPC equivalent with open protocols.
Best way to make your protocol seem like a joke: replace a letter in the protocol you should have used with “JSON”…