Dop boxes are folders in which users have write-only access and the owner of the drop box has read+write. Some time ago I wrote in this forum how it was possible to modify the contents of a file that you had placed in someone elses drop box. I have now found how to delete a file you have placed in someone elses drop box. It's simple, copy the file to the drop box. Te file is now in the drop box you have chosen. To remove the file from this drop box, just use Finder>edit>undo. I accept this is more an intellectual exercise , but it does mean that drop boxes are NOT really Write-Only.