Can anyone tell me a way to tell if the user is dragging a folder or whether they just dragging some items?

I'm coding a function in C# for an Outlook add-in that is triggered by the user dragging one or more items or if they drag an entire folder. If it's a folder they're dragging, I want to be able to loop through all of the items within that folder. If I use the Selection method of ActiveExplorer() this will only return the selected items which is great if the user is dragging emails directly but no good if they're dragging an entire folder as this only returns the emails that happen to be selected within the folder.