Possibility to send e-mail in the future. Few minuts, hours or even years later. You can cancel e-mail before sending date.
- Sending reports in right time (especialy for time difference in the world)
- Sending something and give some time to think about that
- Tell your girlfriend how much you love her for ten years when love is not so strong like now. :)
- Give to other mail services to use it trouth yahoo and earn money.

Technicaly very easy. I couldn't find something like that. I needed it in my web page.