We have configured spam protection with black listing. The system does not block messages are coming from blacklisted IP address. Server would not be rejecting mail from IP’s listed at
Some public DNS providers wisely implement non-hijacked responses for known DNSBL zones like Spamhaus.
Check what DNS resolvers you are using: If you are using a free DNS servers like Google Public DNS, in most cases you will receive a not listed (NXDOMAIN) reply from Spamhaus’ public DNSBL servers. Please use your own DNS servers when doing DNSBL queries to Spamhaus.
In other words, commonly used public resolvers such as Google’s (126.96.36.199 / 188.8.131.52) and 184.108.40.206 – 220.127.116.11 would not work with SpamHaus.
Proper DNS response:
# dig +short TXT 18.104.22.168.zen.spamhaus.org
As workaround you can specify other DNS servers. For example,
OpenDNS Home :