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DNSBL Blacklist Check

Test any IPv4 address against 6 major DNSBLs in parallel — find out if your mail server's IP is on a blocklist that's hurting deliverability. Useful when "my emails are going to spam" might be an IP reputation issue.

Note: This checks public DNSBLs only. If you're trying to find out why your email is being rejected by a specific provider, also check that provider's own postmaster tools (Google Postmaster, Microsoft SNDS, etc.) — those have private reputation systems we can't query.
Status
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About this tool

What gets checked

Six widely-used public DNSBLs are queried in parallel via Cloudflare DNS-over-HTTPS:

  • SpamCop (bl.spamcop.net) — community-fed list, weighted heavily by major email providers
  • Barracuda Reputation (b.barracudacentral.org) — used by Barracuda email security and many enterprise filters
  • PSBL (psbl.surriel.com) — Passive Spam Block List, automatic listing from spam trap data
  • UCEPROTECT-1 (dnsbl-1.uceprotect.net) — single-IP listings (Level 1 only — Levels 2/3 list whole netblocks/ASNs and tend to overshoot)
  • Mailspike (bl.mailspike.net) — multi-tier reputation list with severity codes
  • DroneBL (dnsbl.dronebl.org) — bot, drone, and proxy detection

What's not checked, and why

  • Spamhaus (SBL/XBL/PBL/CSS) — explicitly forbids free public lookup tools per their license terms. To check Spamhaus, use their official checker.
  • CBL/Composite Blocking List — same restrictions as Spamhaus.
  • Aggregator / multi-RBL services — proprietary. Use the source DNSBL pages directly.

How DNSBL queries work

For each blacklist, the tool reverses the IP octets and prepends them to the DNSBL's hostname. For example, checking 1.2.3.4 against SpamCop queries 4.3.2.1.bl.spamcop.net. If the DNS lookup returns NXDOMAIN, the IP isn't listed. If it returns an A record (typically 127.0.0.x), it is listed — and the specific code tells you why.

If you're listed — what to do

  • Click the DNSBL name in the results to go to its delisting page. Most have a public form.
  • Find and stop the source. A listing usually means a compromised account, misconfigured mail server (open relay), or compromised customer device sending spam. Delisting without fixing the root cause means you'll re-list within hours.
  • Check authentication first. Make sure SPF, DKIM, and DMARC are correctly configured for your domain — use the Email Health Check to verify. Authenticated mail is much less likely to land on these lists.
  • Warm up new IPs gradually. Sending high volume from a fresh IP is the fastest way to get blacklisted; ramp up over weeks.

Privacy and rate limits

Lookups are made server-side via Cloudflare DoH — your browser doesn't directly query DNSBLs. Results are edge-cached for 5 minutes per IP to keep query volume low against the upstream lists, who provide free public access on the assumption that automated tools behave responsibly.

Barracuda Central data is provided by Barracuda Networks. DroneBL is operated by the DroneBL team. PSBL is run by Surriel. All other lists are property of their respective operators — see the homepage links above for details.
When this is most useful

If a customer says "my emails to Gmail are bouncing" or "everything I send goes to spam," check their sending IP here first. If you see a listing on SpamCop or Barracuda, that explains the problem. If everything's clean, the issue is more likely SPF/DKIM/DMARC misalignment — the Email Health Check tool will find that.