Okay, I better see the usefulness of the 'move to' drop-downs. But I think they make the interface confusing and a little scarier so I'd default to not having them, allow users to choose to have them, and, when reporting search results not restricted to a single folder, use text to indicate which folder the message is in if the drop-downs are not enabled. (I wouldn't sort results based on folder -- I'd rather keep them sorted by date.)