Free diagnostic

Email blacklist checker for IPs and domains.

Query more than 20 public DNS blocklists for a sending IP or domain, decode each listing's return code, and get the direct delisting link.

Run blacklist checkBlacklist removal playbook

20+

blocklists queried

IP+domain

input types

0

stored submissions

What a blacklist check can prove

DNS blocklists are reputation lists queried over DNS. This tool checks a sending IPv4 address, or a domain's A record, against the lists that actually affect delivery, plus informational lists that occasionally surface real problems. Domain input also queries the Spamhaus DBL domain blocklist.

  • Every listing is decoded: the return code and what the list operator says it means.
  • Each listing links to the operator's own lookup or delisting page.
  • High-impact lists (Spamhaus, SpamCop, Barracuda, CBL) are separated from informational ones.

What it cannot prove

A clean result does not guarantee inbox placement, and a listing on an obscure list is not a delivery emergency. Reputation also lives in provider-private systems (Gmail, Outlook) that no public DNSBL covers. Pair listings with complaint, bounce, and authentication evidence before acting.

Fundamentals

What is an email blacklist (DNSBL)?

A DNS-based blocklist is a reputation database published as DNS records. A receiving mail server takes the connecting IP, reverses it, and asks the list's zone — if the zone answers with an address in the 127.0.0.0/8 range, the IP is listed. The lookup takes milliseconds, which is why blocklists became the cheapest first-line filter in email. Lists are not equal. Spamhaus ZEN is used by a large share of receiving infrastructure, so a listing there translates directly into rejections. Barracuda, SpamCop, and the CBL matter for specific receiver populations. Many other lists are regional, stale, or aggressive by design — a single listing on one of those is a signal to investigate, not a five-alarm fire. There are also two different objects to check. IP lists cover the server that connects to receivers. Domain lists — the Spamhaus DBL is the important one — cover domains that appear in message bodies and links, which is how a shared-IP sender can still be blocked over a bad link domain. This checker queries both.

Reading the output

How to read your results

Enter a sending IPv4 address or a domain. Domain input resolves the public A record and checks that IP, then also queries the domain blocklists. The summary shows how many zones were queried and how many returned a listing.

  • list: the zone that reported the listing. High-impact lists — Spamhaus ZEN, SpamCop, Barracuda, CBL — affect mainstream delivery; informational lists mostly do not.
  • codes: the raw 127.0.0.x answers the zone returned. For Spamhaus, 127.0.0.2 is the SBL (spam sources), 127.0.0.3 is CSS (snowshoe operations), 127.0.0.4 is XBL (hijacked hosts), and 127.0.0.10/11 is the PBL (space that should not send direct SMTP).
  • meaning: the decoded explanation of those codes, so you know whether you are dealing with a spam-source listing or a hijacked-host listing — the fixes differ.
  • delistUrl: the operator's own lookup or removal page. Always confirm the listing there before requesting removal; third-party tools (including this one) are a first look, not the source of truth.

Troubleshooting

Common errors and how to fix them

Delisting without fixing the cause is the most common mistake — most operators relist within hours, and repeat requests lose credibility. Work the cause first, then appeal.

  • Listed on the PBL (127.0.0.10/11): your IP is in space the provider marks as end-user. The fix is usually to relay through your ISP's or ESP's smarthost instead of sending direct-to-MX.
  • Listed on the XBL (127.0.0.4): a machine behind your IP is compromised and sending spam. Find it — check connection logs and unexpected SMTP traffic — before requesting removal.
  • Listed on SpamCop: driven by user complaints and spamtrap hits. Listings expire on their own once the traffic stops; find the campaign or form that generated the complaints.
  • Listed on UCEPROTECT or similar aggressive lists: these escalate to range-level listings quickly and most large receivers ignore them. Verify whether the listing actually affects your recipients before spending time on it.
  • Domain listed on the DBL: a domain in your message content or links is the problem, not your IP. Audit tracking domains, link shorteners, and any domain you redirect through.
  • Shared-IP listing: on shared ESP pools, another customer's behavior lists the IP you share. Report it to the ESP — only they can fix pool reputation.

Providers

Per-provider notes

Public blocklists are only one reputation surface. The large mailbox providers keep private systems that no public tool can query, so a clean result here does not mean Gmail or Outlook trusts you.

  • Gmail: does not publish a blocklist and rarely leans on public DNSBLs directly. Use Google Postmaster Tools for its domain and IP reputation instead — see the Postmaster walkthrough.
  • Outlook / Microsoft 365: maintains its own blocklist plus sender support delisting. Watch Microsoft SNDS for complaint and trap evidence alongside public lists.
  • Yahoo: combines its own complaint data with authentication requirements; public listings are secondary to complaint rate and DMARC enforcement.
  • Corporate filters (Barracuda, Proofpoint, Mimecast): these are where mid-tier public lists actually bite, because appliances query them at the connection level.

Comparison

WillItInbox vs MXToolbox vs dmarcian

MXToolbox popularized the one-off blacklist lookup and offers paid monitoring from $129/mo; dmarcian is a paid, DMARC-focused suite. WillItInbox runs this checker free with no login and no retention of what you submit, and the same listing evidence feeds domain monitoring when you want to be alerted instead of checking by hand. For the full delisting workflow, read the blacklist removal playbook.

CapabilityWillItInboxMXToolboxdmarcian
One-off blacklist lookupFree, no login, IP + domainFree, ad-supportedNot the product's focus
Decoded return codesYes, with delist linksPartialNo
Domain blocklist (DBL)Checked for domain inputSeparate toolNo
Listing alerts over timeDomain monitoringPaid plans from $129/moDMARC-focused plans
Submitted-data retentionNoneVaries by productVaries by product

Live diagnostic

Check current evidence

This anonymous tool is rate limited and does not retain submitted input. It reports observable evidence without promising delivery, authentication alignment, or inbox placement.

No SMTP mailbox probing, account lookup, or tenant data is used.

Enter an input to see current evidence, limitations, official references, and the relevant next step.

Related

Blacklist removal playbook

Which lists matter and the exact delisting order of operations.

Domain monitoring

Track blocklist and DNS drift over time instead of one-off checks.

SNDS guide

Read Microsoft's own reputation evidence alongside public lists.

Monitor a domain

Get alerted when a listing appears, not weeks later.

FAQ

My IP is listed on one small list. Should I panic?

No. Check whether the list is actually used by your recipients' providers. Spamhaus, SpamCop, Barracuda, and CBL listings deserve immediate action; many other lists are informational. A single obscure listing with no delivery failures is a watch item, not an emergency.

How do I get delisted?

Fix the cause first — compromised sender, dirty list, misconfigured forwarder — then use the operator's own removal page (linked in each result). Confirm the listing there, state what you fixed, and request removal once. Requesting delisting before the cause is fixed usually gets you relisted and deprioritized.

Why does the checker reject my IPv6 address?

The established public DNSBLs are IPv4 lists — their zones do not publish IPv6 listings in a compatible format. Checking an IPv6 address against them would produce a misleading clean result, so the tool refuses instead.

Does a clean result mean my email will reach the inbox?

No. Public blocklists are one reputation input. Gmail, Outlook, and Yahoo run private reputation systems that no public tool can query, and content, authentication, and engagement all feed placement. Treat a clean result as 'no public-list blocker', then check provider dashboards and run a real message test.

What is the difference between an IP listing and a domain listing?

IP lists cover the server connecting to receivers; domain lists (like the Spamhaus DBL) cover domains inside the message content and links. You can be clean on one and listed on the other — senders on shared IPs are often blocked over a bad link domain instead.

Do you store the IPs or domains I check?

No. The tool is anonymous, rate limited, and keeps nothing you submit. Each query is resolved live against public DNS and discarded.