Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!

Mailvelope - Mailvelope open source project. OpenPGP in your browser.

Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.

ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.

Mailspring - Mailspring is a mail client for Mac, Windows and Linux.

ProtonMail Extension - Unofficial webextension for ProtonMail