E-mail is a system to asynchronously deliver messages to a set of recipients. That's it ; there is nothing you can do to force the messages to get deleted (the

E-mail is a system to asynchronously deliver messages to a set of recipients. That's it ; there is nothing you can do to force the messages to get deleted (the same way read receipts don't work). However, I agree that an advisory expiral date such as "Not-Relevant-After" could be useful if you're way behind your email inbox.