Mailvelope é um novo plugin de navegador que fornece criptografia OpenPGP para o Gmail / Google Apps, Outlook, Yahoo e GMX. De acordo com Lifehacker :
Mailvelope is in beta, and there's a full extension available for Chrome, and an early beta available for Firefox, but when we tested it both extensions worked well. Gmail/Google Apps, Outlook, Yahoo!, and GMX are all supported, and the app can be configured to support others. After installing the extension, you can generate your own public and private keys to use to encrypt messages in the extension's preferences. Once your keys are ready, the next time you compose a message, you'll see a lock in the compose window that you can click to encrypt your message. You can even use multiple keys for multiple recipients.
When you get an encrypted message, the process works in reverse. You'll see the encrypted message with a lock overlay over it, and you can click it to enter your key password. Mailvelope will search your saved keys to find the one needed, and decrypt the message for you.