K9 is by far the best email client I've found for Android. I'm glad for its open-source nature as it helps to be secure in the knowledge that my email is not being listened-in-on, as well as other more advanced features such as E2EE via PGP encryption.

It's simple to use and it has a lot of options to configure your emails.

One of the few email clients POP and IMAP, for Androida. In my opinion, the most adequate.