Side bar category for items awaiting 3rd party action (i.e. messages left, emails sent, etc.)

Would it be possible to have a side bar list / pending list for messages left or emails sent, and awaiting response?  That way they can be dragged back to another day for action if they sit too long unanswered, or marked as completed when the information / response is received.  It would be nice to have something specifically for 3rd party action, instead of cluttering my pending list which relies solely on my action.