emails

Emails client

Claws Mail GPL@claws-mail.org: http://www.claws-mail.org/releases.php

An email client and RSS reader, based on GTK+, featuring extensibility, robustness and stability

MailBird

IMAP and POP3 email client, featuring customization, complete touch support and multiple language support.

Nylas N1

An extensible desktop mail app built on the modern web.

Thunderbird MPL@mozilla.org: https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Source_Code/Getting_comm-central

also Mozilla Thunderbird

Email client with minimalistic design with powerful address book, emails filter, RSS reader, etc.