Ok, I'm going to assume that you're using debian (if not you'll need to install it manually after downloading from postgrey.schweikert.ch/
) and of course have postfix installed and configured.
apt-get install postgrey
You don't have to but I like to reduce the greylisted time from around 6 mins to 25 - this means that genuine senders are not waiting for an extended amount of time for their emails to arrive:
sed -i 's/--inet=127.0.0.1:60000/--inet=127.0.0.1:60000 --delay=29/' /etc/default/postgrey
We then add the necessary information to the postfix config:
postconf -e "smtpd_restriction_classes = check_greylist"
postconf -e "check_greylist = check_policy_service inet:127.0.0.1:60000"
We can add exceptions to the grey listing (both sender email addresses and networks/ip address). First, we create the files we need to do this:
cp access greylist_sender_exceptions
Then we add the files to /etc/postfix/main.conf:
Let me know if you need any further information or you meet with any issues.