Mozilla halted development of Thunderbird 10 years ago (2012) and it has been community run ever since.
https://www.theverge.com/2012/7/6/3142046/mozilla-halt-furth...
I mean they are putting resources toward it by hiring the main dev which is a good start.
Thunderbird on the desktop is over 200mb these days, so it will be interesting to see if k9 can avoid turning into a chungus on my phone.
Pro-Tip: Enable desktop mode promptly after clicking the bookmark in your browser. If you're fast enough, you may not get the App-Nag-Screen© and have a short wait for the bloat to load. YMMV.
I hope this behavior does not infect K-9 Mail.
I want a mail client that connects to my mail server and nothing else. Any functionality that involves connecting to anyone or anything beyond that is unwanted.
You'll note that client IP is coarse location. Any service that has persistent identifiers and is contacted daily gets your travel history.
Need I go on?
Right now there's Geary, which is OK for what it is but quite limited and basic. I imagine that either mobile-friendly UI for Thunderbird and Linux non-Android K-9 would be quite serious efforts, though.