outlook folder permission

I have a tricky condition where i am confused to asssign the folder permission.My requirement is that, the users can drag drop mails inside folders of a mailbox but cant delete any mails from it. so as per this scenario, what whould be the suggested outlook folder permission?

 I know that, for this scenario, the answer wont be default type like: editor, publishing editor etc; it will be custom. but i would like to know the settings tick options in outlook folder permission.