> The final launch will be Thundermail, an email hosting service using the open-source Stalwart stack. Users will be able to pick between thundermail.com and tb.pro domains.

If the article is correct, Thundermail will be built using Stalwart[1], which appears to support JMAP

[1]: https://stalw.art/

Yes! I'm a fastmail user and every couple of months I do a survey of JMAP support and come back disappointed.

Speaking about thunderbird, I liked their UI redesign, but it seems they are taking away quite a bit of plugin capabilities, e.g. there used to be the possibility to run firenvim (a plugin to run neovim in the compose window), but that's not possible anymore.

Is it just JMAP, or why does Fastmail's web app feel so fast? I have moved away from all locally running mail apps to Fastmail and even fetch/alias all my other mail accounts to them because of the much better experience.