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DNSBL Error Code - Open Resolver
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This page regards queries to a Spamhaus DNSBL made from a DNS resolver.

A return code of to a query made to Spamhaus public zone servers indicates that the query was made via a public open resolver, that is, a DNS resolver which will answer queries for anyone. Examples of such open resolvers are (Cloudflare), (Google), or (Quad9).

Spamhaus does not permit queries from such public DNS resolvers. If your queries receive that return code, you will not get any effective use of Spamhaus data. To obtain effective use of Spamhaus data, please query Spamhaus public zone mirrors from a private IP address which meets Spamhaus DNSBL Usage Terms.

A Spamhaus DNSBL return code of must not be used to reject email, nor for any other blocking or filtering application of any Internet traffic. That return code only indicates that the DNSBL query was made via a public open resolver.

Spamhaus DNSBL Usage FAQ has further information about Spamhaus DNSBLs, open resolvers, and return codes.

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