Could you take a look at Claws Mail? https://www.claws-mail.org
As far as I can tell, it seems to have no telemetry; the only real drawback is defaulting to sending the user agent of Claws Mail and its version string, but this can be trivially disabled and is much better than the things that lay hidden in Thunderbird.
Yeah sure! I actually use claws-mail along side with mutt sometimes. I'll have to retest it but several months ago the mail client was completely silent.
Deleting a branch is permanent. It CANNOT be undone. Continue?