Tools
IP blacklist (DNSBL) checker
Check an IP address against the major public DNSBLs in parallel. We correctly distinguish actual listings from Spamhaus-style 'refused public resolver' responses, so a clean IP never shows up as falsely listed.
About the lists
Each major receiver (Gmail, Outlook, Yahoo) decides independently which DNSBLs to consult. Spamhaus is the most-cited; the others are mixed into different blends. An IP listed on Spamhaus is in real trouble; an IP listed on three minor lists may not be affected by most receivers.
Why Spamhaus shows "refused"
Spamhaus and several other large lists refuse queries from public DNS resolvers (Cloudflare 1.1.1.1, Google 8.8.8.8) because their free tier requires per-resolver enrollment. Browsers querying via DNS-over-HTTPS hit those resolvers, so the response is a refusal code (in the 127.255.X.X range), not a real listing. We classify these as refused, not listed — anything else would ship false positives for every IP queried.
To get a real Spamhaus answer, run dig YOUR.IP.REVERSED.zen.spamhaus.org from your own resolver (a corporate DNS, your ISP's resolver, or a private resolver you operate). Spamhaus's web checker at check.spamhaus.org uses their own infrastructure and returns the authoritative answer.
Worried about your sending IP?
SNDR runs a multi-MTA pool with per-recipient-ISP routing and circuit-breaker drop-out for misbehaving boxes. Reputation across the pool is monitored continuously. Start free.