First off, your bumps are awesome haha. Secondly, I support this idea. This could be potentially beneficial to active traders, guild leaders/co-leaders, and those who are on any of the various helper lists (they are bound to be PM'd about the subject they are assigned as a helper to). Breaking these up into different sections could keep users far more organized and it would give them the ability to prioritize private messages (if they have bulk messages). Not to mention, the staff team will benefit greatly off this. You're right, they get hundreds of message daily. So the ability to prioritize private messages via folders would be so helpful to the staff team.

You've got my vote.