Noted and respected spam filterer Spamhaus is indicating that they believe the the Protected Sky ( blacklist is "fraudulent." They report that Protected Sky is "an anonymously-run DNSBL service which was pirating [Spamhaus] data and republishing it as its own work." Spamhaus further indicates that Protected Sky doesn't follow DNSBL best practices as indicated in RFC6471.

That, plus the fact that nobody seems to know who runs this blacklist, plus these allegations over data theft, should be enough to give any email administrator pause when considering whether or not to use this blacklist in their mail server configuration.