Adding DNSBL to Postfix can be a great advantage as these services will help you defend against email spam. What these services does, is to provide a realtime database over IP addresses that are sending spam. If Postfix gets a positive result looking at a certain IP address, it will reject that mail.
Installation is simple, you just need to edit the main.cf file of Postfix.
Edit the line starting with
smtpd_recipient_restrictions = ...
In the end of that line before “permit” insert content like this
, reject_rbl_client cbl.abuseat.org, reject_rbl_client bl.spamcop.net, reject_rbl_client zen.spamhaus.org
Reload Postfix to load the new rules
You can specify as many DNSBL servers you like.