I'm not sure has this been suggested.
So, with a couple friends in the game, we came to a conclusion that the game would need a private messaging system for the players. At times people tend to be away from the game and may miss some important things others have said, aswell that people aren't always same time online and the chat also flows very fast at times. So the ability to send private messages and read them from a message box, when the other side isn't online, would be really helpful. That could be used for messaging between players in distant timezones who can't be online together much, reminders, important messages, aswell for notifications/warnings from game admins/mods.
Would do us all good, don't you think?
~Monarth