If Spam Blockers DNSBL servers are not accessible you may receive warnings in the user interface. Though access to these servers is not required, the detection rate is significantly improved when using them.
More info on DNSBL: http://en.wikipedia.org/wiki/DNSBL
The script at the bottom of this page will run and test each of the currently configured upstream DNS servers against the multiple DNSBL servers used by Spam Blocker and Spam Blocker Lite.
First it will test queries against the local Untangle server which will use whatever upstream DNS and local DNS servers you have configured. Next it will test each server individually.
Some commonly used servers (like 18.104.22.168) provide inconsistent results. Sometimes queries will pass and sometimes they will fail. Running the script several times is succession may provide more accurate results in this case.
How to Run
From the command line on your Untangle NGFW:
curl -s http://www.untangle.com/download/patches/generic/check_spam_health.sh | bash