Secure/Multipurpose Internet Mail Extensions (S/MIME) is a standard public key encryption protocol for e-mail. Gmail S/MIME is a free Firefox add-on that lets users send and receive encrypted e-mail via Google Mail from inside Firefox. It secures your e-mail messages so that only recipients with valid digital certificates can open and read them. To use Gmail S/MIME, you must have a digital certificate validating your identity for your accounts. These are available for free online, and they're easy to install, usually via a wizard. Both users need secured e-mail to open each other's messages; recipients who lack proper certification will be unable to open and read your encrypted messages.
Gmail S/MIME installs and downloads like most Firefox add-ons. We restarted Firefox and opened the add-on's Options, which mostly deal with how the program signs and stores messages, though there's an SMTP Options configuration pop-up and a button to display Gmail S/MIME's license. We selected the check box to automatically import certificates from signed messages, since we planned to send secure messages between several accounts to test the add-on. After making sure our certificates were squared away, we opened Gmail and composed a new message. We entered an address of an account that had certification and clicked the tiny padlock icon on the Gmail message. We clicked send, and a pop-up advised us that our secured message had been sent. We opened our usual e-mail client and received the encrypted message, which was not displayed in the preview pane. We clicked to open the message, and a pop-up asked us for a password. We entered the correct password, and our message displayed normally. We were able to reply securely to the sending account as well as our other Gmail accounts sharing our Google master account.
Gmail S/MIME made it easy to send and receive secure messages directly from Firefox via Gmail. It adds another layer of security to Web-based e-mail, which continues to add capabilities at a rate that could drive standalone e-mail clients into obsolescence sooner than expected.