I have two requests/ideas, one for mail and the other for any chat window.
The first is to mark the sent mail with the date and time so the recipient has some idea how long it's been since it was written. We usually do this when we write mail, it's now automatically done in email. The other is to add chat commands like in IRC to any chat window. Like LIST USERS or TIME UNTIL SERVER RESET although the last one shouldn't be required once the game's no longer in beta. Stuff like that.
One command idea I had would be to create some chat commands, like #laugh, that would be linked to avatar expressions so you don't have to change focus from a chat window, like local chat, to make the avatar laugh, look horrified or look angry.