Using our public mirrors? Check your return codes now

This notice explains that DNSBL queries performed via public or open resolvers or from IP addresses with generic/unattributable reverse DNS will be blocked (returning code 127.255.255.254). It describes why such queries are disallowed, and provides remediation guidance and alternatives, including correct MTA configuration, using the Spamhaus Data Query Service (DQS), or querying from a dedicated IP with proper reverse/forward DNS.