if you are a small company and you do not care about Sales Teams structure you can remove the persons from the Sales Team... this should stop the emails. I am trying this solution right now as I was always receiving these emails when somebody (from outside of the Sales Team) was creating an invoice...

I do not know if, on the opposite to this, the fact that the user that creates the invoice is not in the Sales Team leads to the creation of the email...

Hello  Angela,

you could try to inherit the sale.order function action_confirm and remove all linked partners (and users) from the message_follower_ids.

          @api.multi
          def action_confirm(self):

              return_value = super(sale_order,           
       
      self.with_context(mail_create_nosubscribe=True)).action_confirm()

              for follower in self['message_follower_ids']:
                  follower.unlink()

              return return_value

Hope this will help you.

Thanks!