docNCRYPT - docNCRYPT is a cybersecurity platform which only focuses on its core services in protecting your email directly from the different email service provider and allows you to integrate your business email portal in the online service.
ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.
Websense Email Security - Websense Email Security is a powerful email protection tool that helps you strengthen the security of your network.
Enigmail - Security extension to Mozilla Thunderbird and SeaMonkey
Cisco Email Security - Cisco Email Security protects against ransomware, business email compromise, spoofing, and phishing.
Mailvelope - Mailvelope open source project. OpenPGP in your browser.