I have a cPanel DNS only server that I have already configured also as a slave backup mx server.
I have configured it to:
1) Allow only specific domains
2) Search multiple RBL's and deny if IP is on a blacklist.
Now I want to take it further by only passing through the active email addresses on the primary server and drop the message if the recipient is not in the whitelist file .
I have created a file which will get updated every 10 minutes which is named /etc/recipients_whiltelisted.
Due to security, we will only provide the exim.conf file.