Unofficial, free and open-source Inbox by Gmail Desktop App. NOTE: This is only to provide appimages, I am not the developer.

Tutanota is an email client with a strong focus on security and privacy that lets you encrypt emails on all your devices. NOTE: This is only to provide appimages, I am not the developer.

ProtonMail Desktop is an unofficial app that emulates a native client for the ProtonMail e-mail service. NOTE: This is only to provide appimages, I am not the developer.

Thunderbird is a free email application that’s easy to set up and customize – and it’s loaded with great features! NOTE: This is only to provide appimages, I am not the developer.

This little tool downloads your emails from an Exchange Server and stores them in a local mbox file. Optionally the mails can be kept on the server. It uses the Exchange ActiveSync protocol. See http://en.wikipedia.org/wiki/Airsync configuration: see airsyncDownload –help

Claws Mail – the user-friendly, lightweight and fast email client!

Manitou-Mail is a 3-part database-driven email system: a PostgreSQL database for the storage engine, a Perl daemon that does send/receive and customizable analysis/indexing of the mail, and a mailer-like user interface (C++/Qt) connected to the database

qCheckGMail is a yet another KDE application that uses gmail atom feed to report if a user has new email in their gmail accounts More screenshots are on the project’s page. Supported features: -The application can be build as a pure Qt tray application or a KDE status item notifier tray…

A Mail Applet for the system tray to watch your Maildir box and get notifications whenever theres a new mail.

A portable Qt4/Qt5 based GMail notifier, which is designed to provide all of the functionality that the official Windows notifier has, and more.