Thanks for asking!
Both Protonmail and Tutanota support custom domains in their Premium versions (sadly).
For Android, K-9 Mail ( @k9mail ) supports POP3/IMAP, and you could use OpenKeychain for PGP.
For PC, Thunderbird Mail does the same as K-9 Mail. You could also add the Extension, "TorBirdy" to connect through Tor.
Again, thanks for asking!