Send LMTP RSET command and process the server response.

def rset(self):
        """
        Send LMTP RSET command and process the server response.

        """
        self._send('RSET\r\n')
        resp = self._read()
        if not resp.startswith('250'):
            logger.warn('Unexpected server response at RSET: ' + resp)
        self._recipients = []
        self.results = {}