K-9 Mail is an open source email client that works with basically every email provider.
Features
* supports multiple accounts
* Unified Inbox
*privacy-friendly (no tracking whatsoever, only connects to your email provider)
* automatic background synchronization or push notifications
* local and server-side search
*OpenPGP email encryption (PGP/MIME)
Install the app “OpenKeychain: Easy PGP” to encrypt/decrypt your emails using OpenPGP.
