Postfix/Blacklisting

Blacklisting is the process of banning specific IP addresses or address ranges from sending email to your server entirely.

Background
In the email server administration world, blacklisting generally refers to using a Realtime Black(hole) List (usually abbreviated to RBL) service operating over the DNS protocol.

There are various RBL services available. A good overview is over at Wikipedia's list of DNS blacklists. Another fairly useful resource is DNSBL.info which allows you to check if your server's IP address block has been listed in any of the major RBLs.

Basically, when a computer asks your system to receive some mail, your system sends a DNS query to the RBL provider(s) including the identity of that sending system. If the system is blacklisted, the response will indicate so, and the mail will be rejected.

Setup
To enable them, add  entries to your  file's   directive based upon the services you have selected, as follows.

Deployment
Finally, tell postfix to reload its configuration for the changes to take effect.