Self deleting email

  Why didn't anyone think of self-destruction/deleting email? Probably 80-90% of emails I get at work during the day are short messages to tell me something and don't require any action...You open them, register some info and either store for future reference, but most of the time you trash it..I know some mail clients (like Novell Groupwise that I'm using) can send delayed emails, so the time interaction module with server is already there. What if you had a check box on your outgoing mail that would trigger self-delete in 1/2/x days after it was opened?
CIA and the White House would love it ;-)
Cheers