Is anyone using alternative open email protocols like JMAP?

I didn't even know that existed! Messing with or self hosting email isn't something I'd even consider, since it's so critical for modern life.

I want something with a 24/7 on call support team, and dedicated specialists running it.

Well, obviously Fastmail does.

And the (excellent!) alternative Mac Fastmail client FMail2 does.

http://fmail-app.fr

No: none of my clients or my mailserver support it.