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IP blacklists — also called DNS-based Blackhole Lists (DNSBLs) or Realtime Blackhole Lists (RBLs) — are databases maintained by anti-spam organisations that flag IP addresses associated with spam, open relays or exploited machines. Mailbox providers query these lists in real time when filtering inbound email. A listing can cause your messages to be blocked at the gateway before they ever reach a spam folder.
Run a free IP blacklist check at spotzee.com/tools/ip-blacklist-check.

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Why this matters

A listed sending IP can block every message you send — not just a single campaign. Unlike domain blacklisting, IP blacklisting often happens overnight after a spam burst, a compromised account or sharing infrastructure with a bad actor. The damage appears immediately and persists until the listing is cleared. For financial services senders, the consequences compound quickly. Transactional alerts, fraud notifications, account statements and compliance emails all originate from the same sending IP. A listing that blocks one blocks all of them simultaneously, creating a customer-communication gap that regulators and customers will notice before your team does. And time matters. Most DNSBL removals take 24–72 hours to propagate after approval. Catching a listing before a send is far cheaper than managing a blocked campaign retroactively.

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How it works

1

Enter your sending IP

Type or paste the IPv4 or IPv6 address of your mail server. Find it in your outbound email headers under the Received: field closest to the sending server.
2

Choose scan depth

Popular checks the most commonly consulted DNSBLs — a fast first check covering the lists most likely to affect inbox placement. Full scans all 69 blacklists in the index, including specialist lists used by enterprise gateways and regional filters.
3

Query each DNSBL via DNS

The tool queries each database using the same DNS lookup method that mailbox providers use when filtering inbound email in real time.
4

Read the verdict

A clean result means your IP is not listed on any checked blacklist. A listed result shows exactly which DNSBLs flagged the address.
5

Act on any listings

Each major DNSBL has its own delisting process. Fix the root cause before submitting — repeated listings lead to longer blackout periods.

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What to watch for

  • Listings on Spamhaus ZEN, SBL or XBL. Spamhaus is the most widely consulted DNSBL suite. A ZEN listing (which combines SBL, XBL and PBL) causes blocking at most major mailbox providers. Submit a removal via spamhaus.org after resolving the root cause.
  • Listings on Spamcop or Barracuda. Both are widely deployed in enterprise mail gateways. A listing here can affect business email delivery even when consumer inbox placement looks normal.
  • Multiple simultaneous listings. Being listed across several DNSBLs at once suggests a systemic problem — a compromised account, open relay or spam burst. Investigate sending logs and authentication configuration immediately.
  • Spamhaus PBL listing. The PBL lists IP ranges that should not initiate outbound SMTP directly (e.g. dynamic consumer connections). It is not a spam listing — it means you need to route through an ESP or a dedicated mail server.
  • Check errors on full scan. Errors usually mean a DNSBL zone was temporarily unreachable. Re-run the check; persistent errors on the same list typically mean the zone is inactive.

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FAQs

An IP blacklist (DNSBL or RBL) is a database of IP addresses associated with spam, open relays or exploited machines. Mailbox providers query these lists in real time when filtering email. A listing can cause messages to be blocked at the gateway. The most widely used IP blacklists include Spamhaus ZEN, Spamcop and the Barracuda Reputation Block List — all checked by this tool.
Each DNSBL has its own delisting process. Spamhaus, Spamcop and Barracuda all provide self-service forms on their websites. Fix the root cause first — spam complaints, open relay configuration, compromised accounts — or the IP will be re-listed quickly. Delisting typically takes 24–72 hours after approval, though Spamhaus PBL removals are near-instant.
The Spamhaus PBL lists IP ranges that should not initiate outbound SMTP directly — typically dynamic home and business connections. It is not a spam listing. If you send through an ESP or a dedicated mail server, PBL has no effect on delivery. It only matters if you run your own mail server on a dynamic or residential IP. Route email through a proper relay instead.
Yes. Not every mailbox provider consults every DNSBL. A Spamhaus listing will affect most providers; a regional or specialist list may only affect a subset of recipients. The check result shows which DNSBLs flagged the IP so you can assess the likely reach of the impact. Prioritise removal from Spamhaus ZEN, Spamcop and Barracuda first.
This guide covers delisting procedures and monitoring cadences in detail. Pair it with the domain blacklist check guide and the SenderScore lookup guide for a complete IP and domain reputation audit.

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Try it

Check any sending IP at spotzee.com/tools/ip-blacklist-check. No sign-up needed for the one-shot web check. Programmatic access deducts a small per-call amount from your Spotzee credit balance — see live per-tool pricing on the Spotzee pricing page.