DNSBL Blacklist Checker
Test an IP address or hostname against 30 well-known DNS-based blocklists in parallel. Get listing status, return codes, and operator links to request delisting.
How to read the result
Each row is one blacklist operator we queried via DNS. A red row means the IP was found in that operator's blocklist — your mail to many recipients is being rejected, deferred, or scored as spam. A grey row is a clean check.
- Spamhaus zones (ZEN, SBL, XBL, PBL) are the most consequential. Listing here typically means immediate hard rejection at major providers.
- SpamCop, Barracuda, UCEPROTECT feed many enterprise mail filters. Listing usually means soft-deferral or spam-folder delivery.
- SORBS, Mailspike, CBL Abuseat are widely used by smaller providers and corporate gateways.
What to do if listed
- Click through to the operator's site (linked in each red row) and look up the listing reason.
- Fix the root cause — open relay, compromised account, snowshoe sending pattern, or shared-IP neighbor abuse.
- Submit the operator's delisting form. Spamhaus typically delists within 1-2 hours; others can take 24-72h.
- Verify with this checker before resuming high-volume sending.
Why we run 30 zones, not just Spamhaus
Different mail receivers consult different blocklists. Yahoo and AOL lean heavily on Spamhaus and their own internal scoring. Microsoft 365 / Outlook checks Spamhaus + SpamCop + Barracuda + several proprietary feeds. Corporate gateways often use UCEPROTECT or SORBS alongside Spamhaus. Checking 30 zones in parallel surfaces issues you would not see by only checking the top three.