Output will be sent to the module logger at INFO level.

def process_message(self, peer, mailfrom, rcpttos, data, **kwargs):
        """Output will be sent to the module logger at INFO level."""
        inheaders = 1
        lines = data.split('\n')
        logger.info('---------- MESSAGE FOLLOWS ----------')
        for line in lines:
            # headers first
            if inheaders and not line:
                logger.info('X-Peer: %s' % peer[0])
                inheaders = 0
            logger.info(line)
        logger.info('------------ END MESSAGE ------------')