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>:10023service postfix reload
