ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.
Vade for Microsoft 365 - Vade for Microsoft 365 is a top-notch email security solution that is specifically aimed to help MSPs protect their networks from adversaries.
Enigmail - Security extension to Mozilla Thunderbird and SeaMonkey
Libraesva Email Security Gateway - Libraesva Email Security Gateway provides enterprise email protection to assist small to large-sized businesses and enterprises to prevent outside attacks on their network.
Mailvelope - Mailvelope open source project. OpenPGP in your browser.
Abnormal Security - Abnormal is a prominent platform that provides accurate and superior cloud-native Email Security.