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IP Blacklist Check

Check an IPv4 address against Spamhaus ZEN, SpamCop and Barracuda DNS blocklists (plus the closed SORBS zone) in parallel and see any listing TXT text.

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About this tool

The RBL Blacklist Check queries an IPv4 against DNS-based blocklists in parallel: Spamhaus ZEN (the umbrella of SBL, XBL, and PBL), SpamCop's bl.spamcop.net, Barracuda's b.barracudacentral.org, and SORBS's dnsbl.sorbs.net. SORBS was shut down in 2024, so its row can no longer show a real listing. Each lookup reverses the IP octets and queries it as a hostname under the RBL zone — the standard DNSBL protocol. Any A record answer is shown as LISTED, NXDOMAIN as CLEAN, and other DNS failures as ERROR. For listed entries the tool also shows the list's TXT record, which usually contains a listing reason and a delisting URL. Use it when your sending IP starts producing 5.7.1 rejections, or when you take over an IP from a previous tenant and want to confirm it isn't already listed. Queries run in parallel from our backend, and the blocklist operators see the lookups as DNS queries.

Why use it

  • Spamhaus ZEN, SpamCop and Barracuda checked in one query.

  • Parallel execution keeps the wall-clock under a couple of seconds.

  • Pulls the listing-reason TXT record so you know what triggered the listing.

  • Distinguishes ERROR (DNS failure) from CLEAN (NXDOMAIN) so you don't get false-clean results.

  • Pairs with SMTP Server Test and Email Header Analyzer for full deliverability triage.

  • No signup, no rate-limit beyond abuse protection — usable in an active incident.

How to use

  1. Enter the IPv4 address you want to check — for example, your sending MTA's public IP.
  2. Click Check blacklists to run the four parallel DNSBL queries.
  3. Review the summary banner — green if clean across all four, red if listed on any.
  4. For each LISTED row, read the TXT text shown under the status — it usually names the reason and a delisting URL.
  5. Visit the delisting page named in that text, follow the list's removal process, and re-test.
  6. If the IP is clean here but mail still bounces with 5.7.1, run the matching SMTP Server Test.

When it helps

  • When recipients return 5.7.1 'listed in DNSBL' rejections.
  • After taking over a public IP from a previous tenant — confirm a clean reputation.
  • When inbound mail to a server you operate is bounced and you suspect the connecting IP.
  • Periodically as a scheduled deliverability audit on every sending IP you control.
  • When migrating a sending IP between cloud providers — verify it isn't pre-listed.
  • While building a sending-IP allowlist for a new mail platform launch.

Examples

Check an IPv4

Input
8.8.8.8
Expected result
The result shows a per-list CLEAN or LISTED status; results depend on the live DNSBL queries.

Read a per-list result

Input
203.0.113.42
Expected result
A live response may show LISTED and a TXT reason or delisting URL for that list.

Interpret the summary

Input
198.51.100.7
Expected result
The summary reports how many monitored RBLs returned LISTED; the count can change between checks.

Tips

  • Spamhaus ZEN is the heaviest-hitting of the four — a ZEN listing usually means broad rejection.
  • SORBS (dnsbl.sorbs.net) was shut down in 2024, so its row no longer reflects a real listing — rely on the other three.
  • Barracuda requires a manual delisting request via their website for most listings.
  • If you're listed on PBL (a sub-list of ZEN), you don't need to delist — just send through an authenticated MTA.
  • Some DNSBLs only list dynamic-IP ranges (PBL); your VPS may be pre-listed without you doing anything wrong.

Frequently Asked Questions

Is the queried IP sent to any third party?
Each DNSBL query is, by definition, a DNS query to that DNSBL's resolver — Spamhaus, SpamCop, Barracuda, SORBS see your query because that's how DNSBL works. We don't store the IP or share it with anyone else.
How does this compare to mxtoolbox's blacklist check?
We query four zones in parallel rather than 70+. Spamhaus ZEN, SpamCop and Barracuda cover many real rejections; the fourth, SORBS, closed in 2024. Ours is also free with no signup.
What does LISTED actually mean for my email deliverability?
It means the list returned an address for your IP, so receivers that use that list may refuse your mail. The blast radius depends on the list — Spamhaus ZEN affects the most receivers. The SORBS row is not meaningful any more because SORBS closed in 2024.
Can this detect a misconfigured MTA?
It detects the symptom (a listing). To diagnose the cause you usually need to pair this with Email Header Analyzer, SMTP Server Test, and your MTA's own logs.
Why does the tool say IPv4 only?
Most DNSBLs predate IPv6 and don't list AAAA addresses. Querying an IPv6 against an IPv4-only zone returns a guaranteed clean result and would mislead you. We restrict input to IPv4 to avoid false reassurance.
What does 'soft fail' mean here?
DNSBLs themselves don't have a soft/hard fail concept — that's an SPF term. A DNSBL query is binary: listed (any 127.0.0.x answer) or clean (NXDOMAIN). What downstream MTAs do with the listing is configurable per receiver.
How do I get delisted from Spamhaus or SpamCop?
Each list publishes a delisting URL in the TXT record we surface. Spamhaus typically requires you to fix the abuse source first; SpamCop expires listings automatically after 24 hours of clean traffic; Barracuda requires a manual request.
Can a clean RBL result still mean my mail will bounce?
Yes. RBL listing is just one of many deliverability signals. SPF/DKIM/DMARC failures, content filtering, sender-domain reputation, and recipient-specific rules all separately reject mail.

Explore the category

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Glossary

RBL
Realtime Blackhole List — a DNS-based list of IPs known for spam or abuse, queried by mail servers to refuse connections.
DNSBL
DNS-based Blocklist — modern term for RBL. Same protocol: reverse-IP queries that return 127.0.0.x for listed addresses.
Spamhaus ZEN
Spamhaus's combined zone of SBL (server blocklist), XBL (exploits), and PBL (policy / dynamic IPs). The most widely used DNSBL globally.
PBL
Policy Block List — Spamhaus's list of dynamic-IP ranges that should not send direct-to-MX mail. A PBL listing is normal for residential IPs.
Listing TXT record
Most DNSBLs publish a TXT alongside the A record explaining why the IP is listed and how to request removal.
5.7.1 rejection
An SMTP permanent rejection code typically returned when an MTA refuses a connection due to a DNSBL listing or sender-policy failure.
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