I have friends that I haven't had a chat with in a while that I'd like to send a letter to without having to wait for them to be online and at the computer in order to catch their attention. I want to let them know when I'm online so that we can try to play together. It would really make things much easier for us.

That being said, it'd be cool if the mailbox/delivery system allowed us to leave messages, too. At the moment, I don't know how to do that.