This is probably the most painful thing on desktop at the moment, because no one gives a s* to desktop mail apps these days.
I recently switched back to evolution from Thunderbird, but where one if great, the other falls short ( in this case, GPG with Evolution is _painful_ ). Geary is... well, not mature, Claws and Sylpheed are a bit too oldschool and mutt is ... well, mutt.
I'd love to see something like Rainloop[1] as a real desktop app. Mailpile[2] is a nice idea, but is nowhere even close to the usability of Rainloop.
As for mail, Thunderbird is not so bad.
I'm still on the very same install, just switched to xfwm4 and tint2, and I'm quite happy.
[1] https://github.com/matzipan/envoyer/blob/master/README.md#re...