greylisting

http://www.howtoforge.com/greylisting_postfix_postgrey apt-get install postgrey /etc/default/postgrey POSTGREY_OPTS="–inet=<ip>:10023 –delay=60" service postgrey start /etc/postfix/main.cf smtpd_recipient_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unauth_destination, check_policy_service inet:<ip>:10023 service postfix reload