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/ Free Tools — Blacklist Lookup

Check your IP against 25 blacklists at once.

Enter a sending IP or domain and we'll query 25 verified DNSBLs in parallel, score your reputation live, and flag every real listing — while honestly telling you which lists can't be checked from a browser. No signup, nothing sent.

Request infrastructure review How blacklists work

Queries 25 verified DNSBLs in parallel over DNS-over-HTTPS. A domain is resolved to its IP first. Nothing is sent or stored.

/ What this checks

A blacklist lookup checks whether your sending IP appears on the DNS-based blocklists that receiving mail servers consult in real time. If your IP is listed on a list a receiver trusts, your mail to that receiver can be rejected, sent to spam, or penalized — so knowing your listing status across many lists at once is the fastest way to find a reputation problem. This tool queries 35+ DNSBLs in parallel and scores the result, with the listings that matter most surfaced first.

It also does something most lookups don't: it tells you when a result can't be trusted. Several major lists block queries from public DNS resolvers, and rather than guess, this tool marks those as not checkable and points you to the operator's own page. A clean score here means clean across every list that could actually be verified — not a false all-clear that hides the lists that quietly refused to answer.

  • Which, not how many

    One Spamhaus listing hurts more than a dozen obscure ones. The detail matters more than the count, so the tool surfaces the high-impact lists first.

  • Fix, then delist

    Delisting without fixing the cause just leads to relisting. Identify the reason, address it, then use the list's removal process.

  • Honest gaps

    Lists that block public resolvers are marked not checkable, not silently passed — so a clean score is a real one.

  • Root cause

    A listing is a symptom — a compromised account, an open relay, a dirty list, or a bad IP neighbor. The fix lives upstream of the list.

/ How DNSBLs work

How does a receiving server check a blacklist?

DNS-based blocklists are clever in their simplicity: they encode a list of bad IPs as DNS records. To check whether an IP is listed, a receiving server reverses the IP, appends the blocklist's domain, and does an ordinary DNS lookup. If the lookup returns an address in the 127.0.0.0/8 range, the IP is listed; if it returns nothing, the IP is clean. The exact address returned often encodes why — a specific code for spam, for a policy violation, for a known exploit. This tool performs exactly that query for each of dozens of lists at once. 

# How an IP is checked against a blocklist
sending IP        203.0.113.5
reversed          5.113.0.203
query             5.113.0.203.zen.spamhaus.org   (type A)

answer 127.0.0.2  ->  LISTED  (the code says why: spam, policy, exploit)
answer NXDOMAIN   ->  CLEAN   (not on this list)
answer 127.255.255.x ->  query refused (public resolver blocked)

Not all blocklists are equal, and treating them as if they were is the most common mistake people make reading a result. The major lists — Spamhaus and its ZEN composite, Barracuda, SpamCop — are consulted by a large share of the world's receiving servers, so a listing on one of them has immediate, broad consequences for your deliverability. Many smaller lists are queried by almost nobody, and a listing on one is closer to cosmetic. A tool that just counts listings encourages exactly the wrong response: panicking over an obscure list while a single major listing is the one actually costing you the inbox. This is why the result here leads with which lists are involved, weighted by how much each one matters.

Blocklists also differ in what they target. Some list IPs that have demonstrably sent spam. Others are policy lists — they list entire ranges that shouldn't be sending mail directly at all, like residential broadband addresses, regardless of whether any specific spam came from them. Others track exploited machines, open relays, or open proxies. Understanding the type tells you what a listing means: appearing on a policy list because you're sending from a residential connection is a different problem, with a different fix, than appearing on a spam list because an account was compromised. The tool labels the category where the list publishes one.

The honest complication is that some of the most important lists deliberately refuse queries from large public DNS resolvers, to protect their free service from commercial scraping. Because a browser-based tool has to use a public resolver, those lists return a refusal code rather than a real answer. The wrong thing to do is treat that refusal as a clean result, which would hand you a false all-clear on the lists that matter most. This tool detects the refusal codes and marks those lists as not checkable, telling you plainly to verify them on the operator's own page. A reputation tool that hides its blind spots is worse than useless, so this one shows them.

When you do find a real listing, the sequence matters more than the speed. A listing is a symptom, and the cause is almost always one of a short list of culprits: an account whose password was compromised and is now sending spam, a server misconfigured as an open relay, sending to spam-trap addresses harvested into a purchased list, or simply sharing a shared IP with a bad sender. Removing the listing before fixing the cause just resets a clock that runs out again. Identify the reason, fix it at the source, and only then use the list's delisting process — which for the major lists is a self-service page, and for minor lists is often just the passage of clean time.

/ Beyond the snapshot

Why is a one-time check not enough for a real sender?

A lookup like this answers one question at one moment: are you listed right now? That's exactly what you want when you're investigating a sudden deliverability drop, and it's the right first move when mail to a particular provider starts failing. But a snapshot has an obvious limit — a listing that appears the day after you check is invisible until the next time you happen to look, and by then it may have been quietly costing you inbox placement for days. For anyone sending production volume, the gap between checks is where the damage accumulates.

This is the difference between a tool and an operation. The tool tells you your status; continuous monitoring tells you the moment that status changes, which is what actually protects deliverability. A good monitoring setup watches the lists that matter on a schedule, alerts the instant a sending IP appears on a high-impact list, and ties the listing back to the sending activity that likely caused it — so you learn that you're listed and, more to the point, why. The faster a listing is caught, the smaller its window of impact and the easier the delisting, because the underlying cause hasn't had time to compound.

The deeper protection, though, is structural rather than reactive. The IPs that rarely get listed in the first place are the ones where the conditions for listing have been designed out: warmed gradually so they never look like a sudden spam source, isolated so a noisy neighbor can't drag them onto a list, monitored continuously so a problem surfaces in hours rather than weeks, and kept clean through list hygiene that never sends to the spam traps that get you listed in the first place. That combination is what dedicated, managed infrastructure provides, and it's why the senders with the best reputations spend the least time running lookups like this one — their IPs simply don't end up on the lists. A blacklist check is how you catch a problem; an operation built to avoid the problem is how you stop needing to.

/ Blacklist FAQ

What is an email blacklist (DNSBL)?
A DNSBL — DNS-based blocklist — is a published list of IP addresses or domains that a list operator believes have sent spam or shown other abusive behavior. Receiving mail servers query these lists in real time as mail arrives: if your sending IP is listed, the receiver may reject the message, route it to spam, or apply a penalty. Different lists have different criteria and different weight — being on a major list like Spamhaus ZEN affects deliverability far more than appearing on a small, obscure one. This tool checks your IP against many of them at once so you see the full picture rather than one list at a time.
Why do some results say 'not checkable' instead of listed or clean?
Several major blocklists, including Spamhaus, block queries that come through large public DNS resolvers to prevent commercial abuse of their free service. Because this tool runs in your browser through a public DNS-over-HTTPS resolver, those lists return a special error code instead of a real answer. An honest tool reports that as 'not checkable' rather than guessing — showing it as 'clean' would be misleading, and showing it as 'listed' would be wrong. When a result is not checkable here, verify it directly on the list operator's own lookup page for a definitive answer.
I'm listed on a blacklist — what do I do?
First, identify which list and why: the tool shows the listing reason where the operator publishes one. Then fix the root cause, because delisting without fixing what caused it just leads to relisting — common causes are a compromised account sending spam, a misconfigured mail server acting as an open relay, sending to spam traps from a dirty list, or sharing an IP with a bad sender. Once the cause is addressed, use the specific list's delisting process; most major lists have a self-service removal page. Minor lists often expire listings automatically after a clean period. The key is sequence: fix first, then delist.
How much does one blacklist listing actually hurt?
It depends entirely on which list. The major, widely-consulted lists — Spamhaus, Barracuda, SpamCop — are queried by a large share of receiving servers, so a listing on one of those has immediate, broad impact on whether your mail reaches the inbox. Many smaller lists are consulted by almost no one and a listing on them is close to cosmetic. This is why a raw count of listings can mislead: one Spamhaus listing matters more than a dozen obscure ones. The reputation score here weights toward giving you a clear signal, but the listing detail is where the real story is — look at which lists flag you, not the raw count.
Does this tool send anything or store my IP?
No. Every blocklist query runs in your browser as a read-only DNS-over-HTTPS lookup, exactly the kind of query a receiving mail server makes. Nothing is sent to our servers, no email is dispatched, and the IP or domain you enter isn't logged. The checks happen between your browser and the public DNS resolver, not through us.

A clean score is a snapshot. Staying clean is the operation.

Catching a listing is the easy part; running IPs that never get listed in the first place — warmed, isolated, monitored, with the root causes designed out — is what we do. Bring us your sending setup and we'll keep your reputation off the lists for good.

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