Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
MailStore - MailStore Home - A 100% free single-private-user desktop solution
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Gmvault - Backup the emails in your Gmail account.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
MailSteward - MailSteward : The Ultimate E-mail Manager for Mac OS X