The ips.backscatter.org is different than other DNS based blacklists. To use ips.backscatter.org, you are not looking for a normal DNS response of an IP address to a reverse IP address lookup. To use ips.backscatter.org, you will need to determine specifically how to have your mail server look at each individual email, parsing specifically the MAIL FROM: header, looking for a value of "" or "postmaster". If you detect those values, you should block or score against that sender.