A feature I have been missing for a long time is a better way to find and track messages marked todo/action. One simple way would be to allow the folder list to mark folders with action messages like it does with folders with unread messages. For instance having another optional column for action messages in the overview or simply adding it to the unread count (perhaps with a different color). E.g. Inbox(5 + 1) with 5 being blue for unread and 1 red for action.