SpamNinja This tool queries all ip networks of a company from Ripe and blocks them. Installation Edit your main.cf: smtpd_client_restrictions = check_client_access cidr:/etc/postfix/cidr_spamninja Then setup spamninja.py as a cronjob Thanks to http://www.blackmanticore.com/040629229fdd3e219551e3e3fd8f2396