Blacklist Check

// What is tested

• One IPv4 address against eight independent DNS blocklists, queried concurrently: Spamhaus ZEN, SpamCop, Barracuda Reputation Block List, SORBS, CBL/abuseat, PSBL, Mailspike and UCEPROTECT level 1.
• Each query reverses the address octets, appends the list's zone and requests an A record — the standard DNSBL mechanism.
• Any answer inside 127.0.0.0/8 is treated as a listing, and the returned address is shown so the list's own response code can be interpreted.
• Answers inside 127.255.255.0/24 are treated as error codes, not listings. Those are returned by lists that refuse queries from public resolvers, and the zone is reported as Skipped.

// Data sources

The eight DNSBL zones themselves

zen.spamhaus.org, bl.spamcop.net, b.barracudacentral.org, dnsbl.sorbs.net, cbl.abuseat.org, psbl.surriel.com, bl.mailspike.net and dnsbl-1.uceprotect.net. Each is queried directly; no aggregator sits in between.

DNS over HTTPS

Cloudflare with Google Public DNS as fallback, carrying every zone query.

// Limits

• IPv4 only. DNSBL coverage of IPv6 is inconsistent across providers and is not attempted here.
• Queries reach the lists through a public resolver, and several — Spamhaus and CBL in particular — decline those. Where that happens the zone is marked Skipped rather than guessed at. Check those lists directly on their own sites.
• Eight lists is not all lists. A receiving mail server may consult others, or maintain its own private reputation data that no public check can see.
• This covers IP-based blocklists only. Domain-based lists (URIBLs), which operate on domains found in message content, are a separate system and are not checked.
• A listing is a snapshot. Lists add and remove entries continuously.