Mutt - Mutt is a small but very powerful text-based mail client for Unix operating systems.

The Bat - The Bat! is a secure desktop email client for Windows, designed to protect your correspondence against third-parties and to save your time.

Alpine - Alpine is a fast, easy to use email client that is suitable for both the inexperienced email user...

Geary - Geary is an email application built for GNOME 3.

Mailspring - Mailspring is a mail client for Mac, Windows and Linux.

Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!