The trouble is that encryption only works if both your e-mail program and your recipient‘s support it. So if, for example, you‘re on Gmail, but your friend uses a Comcast.net e-mail address, chances are your messages will show up unencrypted at the other end, because Comcast doesn‘t have encryption enabled. Google estimates that up to half of the e-mail sent between Gmail and other sites are not encrypted — a situation that could be easily fixed with the right investments, according to a Google employee who declined to be named because he wasn‘t authorized to speak publicly.