How to Setup Grey Listing with Postgrey

Install the Postgrey package:

aptitude install postgrey

Configure the delay and message settings in /etc/default/postgrey:

POSTGREY_OPTS="--inet=127.0.0.1:60000 --delay=180"
POSTGREY_TEXT="Temporarily deferred due to greylisting. Please try again later."

Restart postgrey:

/etc/init.d/postgrey restart

Enable grey-listing policy service in /etc/postfix/main.cf:

smtpd_recipient_restrictions =
  permit_mynetworks,
  permit_sasl_authenticated,
  [...etc]
  reject_unauth_destination,
  check_policy_service inet:127.0.0.1:60000,

Restart Postfix:

/etc/init.d/postfix restart