Do-It-Yourself ‘Mission Impossible’ shenanigans:

How to Send Self-Destructing Messages with Google Docs

Not so tech-savvy?
There are web apps – like Burn Note and Privnote - that offer an easier solution. They essentially create a temporary web page that auto-expires after it has been viewed once. Dashlane is another app that also lets you send encrypted notes from the desktop and the recipient gets 30 minutes of reading time after which the note will vanish forever.