code: def mark_read(user, message):
      
      BackendClass = stored_messages_settings.STORAGE_BACKEND
      backend = BackendClass()
      backend.inbox_delete(user, message)
docs: Mark message instance as read for user.
      Returns True if the message was `unread` and thus actually marked as `read` or False in case
      it is already `read` or it does not exist at all.
  
      :param user: user instance for the recipient
      :param message: a Message instance to mark as read