A security researcher from the Georgia Institute of Technology has invented an encryption system called "Open Book" that 'vaguifies' emails by removing specifics from them.
"It's kind of like when mom and dad are talking about potential vacation spots while the kids are nearby," said Eric Gilbert, who developed the software. "They can't say or spell 'Disney,' or the children will get too excited. So they use other words and the meaning is implied. Instead of 'Disney,' they could say 'have you bought tickets to the place yet.'"
He's built a Gmail plugin which works the same way - it pulls out specific words and replaces them with vague terms instead. The recipient should be able to work out what you're talking about from context, but anyone eavesdropping on the communications would fail to get the full message.
Typical Email Conversations
"As people react more with each other, they don't have to say as much to understand what is being said," said Gilbert. "Open Book uses the same technique. Even though the messages resemble typical email conversations, they're lost in the background noise of the Internet."
During small-scale tests, the recipients were able to correctly work out the missing words and phrases 95% of the time, while only 2% of strangers were able to do the same thing.
While you can't download it and have a go yet, you can go read the paper that Gilbert presented to the ACM Conference on Human Factors in Computing Systems in South Korea earlier this year.