docs: def quit(self):
          """
          Send LMTP QUIT command, read the server response and disconnect.
  
          """
          self._send('QUIT\r\n')
          resp = self._read()
          if not resp.startswith('221'):
              logger.warning('Unexpected server response at QUIT: ' + resp)
          self._socket.close()
          self._socket = None
          self._recipients = []
          self.results = {}