Comment by ryanleesipes

Sign up for the waitlist here: https://Thundermail.com

Also the Thundermail service is based on Stalwart (completely foss). We'll open source any additional relevant bits.

We also released the supporting services:

https://github.com/thunderbird/appointment

https://github.com/thunderbird/tbpro-add-on

https://github.com/thunderbird/thunderbird-accounts