[throw0101b]

> If JMAP is to be successful, having support in Thunderbird is a must have first step. It's not helpful if the same party that provides the mail service provides the frontend as well.

And if you're going to fund development, also put it in Dovecot.

* https://en.wikipedia.org/wiki/Dovecot_(software)

It does seem to be in Cyrus, but I'm not sure what the marketshare of that software is nowadays:

* https://en.wikipedia.org/wiki/Cyrus_IMAP_server

* https://en.wikipedia.org/wiki/Comparison_of_mail_servers