Another interesting feature would be if you could schedule mails to be sent at a particular time maybe, like the 3mindme post which was posted some days ago.
But don't send it at the time we specify - send it out plus or minus two minutes and some change. There's nothing lamer than saying to yourself "Wow, what a nice email about 'thoughts you had today.' It came at midnight - wow, you sure were up late! Oh wait, it came at 12:00:00. What a douchebag."
Well, there is something lamer: if you are the douchebag.