MailStore - MailStore Home - A 100% free single-private-user desktop solution
Spark Mail - Spark helps you take your inbox under control. Instantly see what’s important and quickly clean up the rest. Spark for Teams allows you to create, discuss, and share email with your colleagues
MailSteward - MailSteward : The Ultimate E-mail Manager for Mac OS X
Newton Mail - Newton is a fully featured mail client available for Android, iOS, macOS and Windows.
Gmvault - Backup the emails in your Gmail account.
myMail - myMail is the smart email app for managing all your accounts on iOS and Android.