In my daily e-mail often happens the following scenario: I send somebody an email which describes some problem and requests an action from the recipient. Typically, I wish to ensure that this action was taken, or at least somehow resolved; when this happens, the email recipient should notify me with a response email about what was done, and what was not and why.

But, sometimes emails don't get read by the recipient, or he forgets to reply to me. At the same time, I cannot constantly keep in memory the list of all emails for which I was waiting an answer and still didn't receive it. So I wonder, is there in any email client such a feature which would allow me to somehow mark specific outgoing emails as "demanding reply"? The mail client could in this case notify me if any "demanding reply" emails still aren't replied for a long time.