Sorry for the delay, but the answer was long enough that I turned it into a blog post instead. Feel free to try it out.

Gnus in Emacs, configured to use autocrypt.

Posteo. Happy with them. For client, gnus in Emacs. Have it configured to do Autocrypt too, but almost nobody else on the planet does 🙁

archive.org is great for borrowing old books, that you probably can’t get your hands on otherwise. Just need a bit of research following references to find titles to search for.