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.

This little tool downloads your emails froman 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/Airsyncconfiguration: 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 accountsMore 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.

Console app to get remote Gmail Imap mailby searching on field SUBJECT Header Body...Like:UID SEARCH SUBJECT "foto" SINCE 20-Sep-2013Download all result on local username dir.or How do I backup All Gmail Mail to eml format?this can be helpful

Sample code to send mail attachment & html full QTextDocument + Image.And the Chunked transfer encoding Mail format 2013.