Toolsley PGPigeon - Simple but powerful OpenPGP-compatible message encryption webapp.
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.
GPGTools - Use GPG Suite to encrypt, decrypt, sign and verify files or messages.
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.
Lockbin - Lockbin is a web application for sending private email messages and files.
Websense Email Security - Websense Email Security is a powerful email protection tool that helps you strengthen the security of your network.