Migadu. Yeah*. On the computer, I use mostly aerc (+notmuch), but hop on Thunderbird once in a while; on mobile I use K-9.
* If you are not looking for totally free options (though their cheapest plan is 20€/y and they give 50% discount to students), and if you don't care about email encryption (which you shouldn't).
Migadu has a very good Pros/Cons page, I highly recommend you take a look, even if you're not using or planning to use their service.
Same. Have multiple domains and mailboxes with them, really solid. The thing I love most is probably the catch all address (allows me to effortlessly create "one-shot" addresses) and the plus-addressing automatic folders (i.e. mails to [email protected] automatically go to folder "bar" in mailbox "foo").