content: Right?  And that said, of course there's going to be a time limit for Gmail, and 30 seconds is plenty.  Any more than that and people are likely to complain that "their e-mail takes too long".    If you've sent a message, and someone reads it, and then you remotely delete that message at a later date, whether it's 30 minutes or 3 months--that other user's still had an opportunity to read and duplicate that message in that amount of time--I feel like Gmail's approach is totally different.  This is apples and oranges.