DNSBL / RBL Checker
General-purpose DNS-based real-time blocklist lookup against the domain's IP.
This is one independent signal used by the Domain Security Score, and can also be run on its own for any domain.
Based on: RFC 5782 — DNS Blacklists and Whitelists (DNSBL/RHSBL)
About this validation
General-purpose DNS-based real-time blocklist lookup against a domain's IP.
- Protocol / standard:
- Rules reviewed:
- Sep 6, 2026
SEOTechTests methodology: Data source: a live DNS query against Spamhaus's ZEN zone for the domain's resolved IP, following RFC 5782's DNSBL mechanism. FAIL on a listing; PASS on NXDOMAIN; UNKNOWN on a refused/rate-limited response or unresolvable IP.
Standards and vendor-documented behavior can change. This reflects the source as last reviewed above, not a permanent guarantee.
FAQ
What is a DNSBL / RBL lookup?
A DNS-based Real-time Blackhole List query -- the IP address is reversed and prepended to a blocklist's DNS zone; a returned A record means the IP is listed, per RFC 5782's standardized mechanism.
How is this different from the Spamhaus DBL checker?
This check queries the ZEN zone against the domain's resolved IP address (an infrastructure/network reputation signal), while the Spamhaus checker queries the DBL zone against the domain name itself.
What does it mean if the IP is listed?
The hosting IP has been associated with spam or compromised-host activity -- on shared hosting this can reflect other tenants on the same address, not necessarily this specific domain.
Why can this check return UNKNOWN rather than PASS?
A DNS refused/rate-limited response code, a DNS resolution failure, or a query timeout all report UNKNOWN -- never treated as either a listing or a clean result.