Blacklist Checker

🛡 Deliverability & security

Check an IP address, or a domain’s mail-server IPs, against major DNS blocklists.

No sign-up required Runs on our own infrastructure Also available via API
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Runs on our diagnostic API. We don’t attach your input to an account for these free tools; short-lived rate-limit/security logs may exist, and requests are rate-limited per IP.

A DNS blocklist — a DNSBL or RBL — is a published list of IP addresses and domains that some operator considers a source of spam or abuse. Receiving mail servers query these lists in real time during the SMTP handshake, and a hit can mean your message is rejected outright, deferred, or dropped straight into spam before content filtering even runs. The frustrating part is that you usually find out only after delivery drops. This tool checks an IP or domain against the major lists so you can see a listing the same way a receiver would, and points you at the right removal process for each one.

How a DNSBL lookup actually works

Blocklists are clever in that they reuse ordinary DNS as the query mechanism — no special API, just an A-record lookup. To ask Spamhaus about the IP 203.0.113.10, you reverse the octets and append the list’s zone:

203.0.113.10  →  reversed  →  10.113.0.203 query:  10.113.0.203.zen.spamhaus.org NXDOMAIN (no record)   → not listed 127.0.0.2 / 127.0.0.x  → LISTED (the last octet is a return code)

If the name doesn’t resolve, the IP isn’t on that list. If it resolves to a 127.0.0.x address, it is listed — and the exact final octet is a coded reason. On Spamhaus ZEN, for example, 127.0.0.2 is the SBL (known spam source), 127.0.0.4 the XBL (exploited/compromised host), and 127.0.0.10/11 the PBL (IPs that shouldn’t be sending mail directly at all). We query 35+ lists in parallel and translate those return codes into plain reasons.

IP lists vs. domain/URI lists

Not every list checks the same thing, and conflating them causes needless panic:

  • IP-based lists judge the sending server’s address. Major ones include Spamhaus ZEN (the combined SBL/XBL/PBL zone, the single most widely enforced list), Barracuda, SpamCop, SORBS, SpamRats and the UCEPROTECT levels.
  • Domain / URI lists judge names rather than addresses — typically the domains that appear in a message body or its links. These include Spamhaus DBL, SURBL and URIBL. A domain can be listed here while every one of its mail IPs is clean, and vice versa.

Because of this split we report IP results and domain/URI results separately. A domain isn’t “blacklisted” just because one of its mail IPs shows up on an IP list — they’re answering different questions.

Why IPs and domains get listed

Listings are rarely arbitrary. The common causes:

  • Spam-trap hits. Operators seed dead or never-valid addresses (spam traps) across the internet. Mailing one — usually a sign of poor list hygiene or purchased data — is a fast way onto a list. Clean lists with the email verifier before sending.
  • A compromised or abused host. A hacked server, a malware-infected machine, or an open relay sending spam without the owner’s knowledge lands on exploit lists like the Spamhaus XBL.
  • Poor or missing reverse DNS. IPs with no PTR or generic, dynamic-looking rDNS get listed by lists such as SpamRats. Check yours with the reverse DNS checker.
  • A cold or reassigned IP. A brand-new sending IP with no reputation, or one previously used by a spammer before it was reassigned to you, can inherit a listing.
  • Complaint volume. Too many recipients hitting “this is spam” feeds complaint-driven lists like SpamCop.

What a listing does — and doesn’t — mean for delivery

Impact varies enormously by list. Spamhaus ZEN is enforced by a large share of the world’s mail servers, so a listing there genuinely blocks mail. Aggressive or collateral-damage lists (UCEPROTECT Level 3, which lists entire ISP netblocks) are widely ignored, so a hit there may cost you nothing. Read which list flagged you before reacting. And remember a clean result is necessary but not sufficient: inbox placement also depends on SPF/DKIM/DMARC authentication and alignment, domain reputation, content and recipient engagement — signals no public blocklist exposes.

How to get delisted

  1. Fix the root cause first. Delisting before you’ve stopped the spam source, closed the open relay, cleaned the compromised host or fixed reverse DNS just gets you relisted — often faster, and sometimes with a longer penalty.
  2. Confirm the fix. Verify rDNS forward-confirms, authentication passes, and your list is clean. The email health check is a fast way to sweep the sending side.
  3. Use the operator’s removal page. Where we find a listing, each row links to that provider’s official removal form. Some lists auto-expire after a quiet period; others require a manual request.
  4. Warm up and go slow. After delisting, ramp volume gradually so you don’t trip the same threshold again.

Every list we check has its own detail page with specific, sourced delisting steps — browse the full blacklist directory to read about each one. Spamhaus also documents its policies at spamhaus.org, and the industry best practices behind all of this come from M3AAWG.

Inbound vs. outbound — read the result carefully

When you enter a domain, we resolve its highest-priority MX and check that IP — the server that receives mail for the domain. If you send marketing through a different provider (Amazon SES, SendGrid, Google, your own relay), that sending IP is not what’s checked here. To check your outbound reputation, enter the actual sending IP. The result explicitly labels the resolved target and its type so there’s no ambiguity. Lists that time out or block our query are reported as “No reply” rather than counted clean — many operators block automated or public-resolver lookups, so use the operator’s own page for a definitive answer.

Frequently asked questions

Does a blacklist listing always block my mail?
No — impact depends on the list and who uses it. Spamhaus is widely enforced; some aggressive lists (e.g. UCEPROTECT L3) are often ignored. Check which list and how it’s used.
Why is my IP clean but mail still goes to spam?
Blocklists are one signal. Placement also depends on authentication, domain reputation, content, engagement and each provider’s own reputation systems. Clean IP ≠ guaranteed inbox.
Why does my checker say “No reply” for some lists?
Some operators (Spamhaus, SORBS…) block automated queries, so we report “No reply” instead of a false “clean.” Use the operator’s own lookup page for a definitive check.
How do I get delisted?
Fix the root cause first, then follow each list’s removal process. Every list has a detail page with specific delisting steps.