Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Gammadyne Clyton - Clyton is an email client with advanced security and spam filtering features.
Mutt - Mutt is a small but very powerful text-based mail client for Unix operating systems.
Nextcloud Mail - 💌 Mail app for Nextcloud