code: def new_connection(self, remote_ip, remote_port):
          
          self.state.set_state('new')
          self._message = Message(Peer(remote_ip, remote_port))
  
          decision, response_sent = self.is_allowed('accept_new_connection',
                                                    self._message.peer)
          if decision:
              if not response_sent:
                  self.handle_input('greet')
              self._set_size_restrictions()
          else:
              if not response_sent:
                  self.reply(554, 'SMTP service not available')
              self.close_connection()
docs: This method is called when a new SMTP session is opened.
          [PUBLIC API]