This is REALLY cool news. This will make them the second JMAP compatible vendor and the first that didn’t invent it (which is an ick)!

This makes it MUCH more interesting to build JMAP clients. I will most likely subscribe to this just to play around with JMAP because I‘ve been to lazy to set up Stalwart for myself.

I wonder whether they will build a new web front-end, since the existing FOSS ones I’m aware of aren’t all that great.

Site is here with waitlist signup. It's also titled "For Those Who Know" and says: >> status beta_signup.is_open=true so perhaps theres a CLI or hidden way to signup immediately?

I don't think people want to change email addresses very often. How do I know Mozilla will still be doing this in 5-10 years? (Edit: Others have pointed out that, if we can bring our own domains, technical users can retain their address. However, for non-technical users that's not an option.)

Also, I'm not sure about charging a fee at the start (except for TB contributors) and providing a free tier later - reverse of the usual way of launching a product. Maybe this is a soft launch to shake out the bugs and build a little momentum, and you can pay if you want to take part?

Mozilla could do something awesome here. I hate to say it, but here is a chance to start fresh and make big, legacy-breaking changes to Thunderbird. The new audience - which should become the vast majority if they are successful - won't care if it's not like the old Thunderbird (possibly unlike many on HN). Here is a chance to do something special and the mail client is all most users see or understand.