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Check an IP or Domain Against Spam Blacklists
The Tools Kit’s free Blacklist Checker tells you whether an IP address is listed on four well-known email blocklists: Spamhaus ZEN, SpamCop, Barracuda Reputation and SORBS. Enter an IPv4 address, or a domain that is resolved to its IP, and every list is queried in parallel, with each result shown as Listed, Clean or No answer.
A blacklisting is one of the most common reasons outgoing email bounces or lands in spam, because many mail servers consult these lists before accepting a message. If you are not sure which address your traffic leaves from, the IP checker shows your current public IP, which you can paste straight into this IP blacklist check.
How to Use the Blacklist Checker
- 1
Enter an IP address or domain
Type an IPv4 address such as 192.0.2.25, or a domain name such as example.com, into the IP Address or Domain box.
- 2
Run the check
Click Check Blacklists or press Enter. A domain is first resolved to an IPv4 address through a live A record lookup, and the first address returned is the one checked.
- 3
Read the summary
The summary line says how many of the four blacklists list the IP, warns you if any did not answer, or confirms it is not listed on any of them.
- 4
Review each blacklist
Each row shows Listed, Clean or No answer for Spamhaus ZEN, SpamCop, Barracuda Reputation and SORBS, with the DNS zone that was queried.
The check needs no account. Because blocklists are queried over DNS, the lookups run on the site’s server through Google Public DNS rather than in your browser.
How a DNSBL Lookup Works
A DNS-based blocklist (DNSBL) publishes its list through ordinary DNS. To ask whether an address is listed, you reverse its four octets, append the list’s zone, and look up an A record for the result. Take the documentation address 192.0.2.25:
| Blacklist | Name queried for 192.0.2.25 |
|---|---|
| Spamhaus ZEN | 25.2.0.192.zen.spamhaus.org |
| SpamCop | 25.2.0.192.bl.spamcop.net |
| Barracuda Reputation | 25.2.0.192.b.barracudacentral.org |
| SORBS | 25.2.0.192.dnsbl.sorbs.net |
If a name returns an A record, usually an address in the 127.0.0.x range, the IP is on that list and the tool shows Listed. If it returns nothing, the tool shows Clean. If the lookup itself fails, the row reads No answer and the summary flags the whole result as incomplete instead of quietly calling it clean. You can run the same kind of query by hand with the DNS lookup tool by choosing the A record type and typing the reversed name.
Reversing the octets is the same trick reverse DNS uses to map an address back to a name. Mail servers often check that too, so it is worth confirming your sending IP has a sensible hostname with the reverse DNS lookup.
Checking a Domain vs Your Mail Server IP
When you type a domain, the checker resolves its A record and tests the first IP that comes back. For most domains that is the web server or a CDN, which is often not the machine that sends your email. To check the right address, look up the domain’s MX records with the DNS lookup, resolve the mail host to its IP, and enter that IP here. If you send through a provider such as Google Workspace or Microsoft 365, the relevant address is in the Received headers of a message you sent.
This tool checks IP-based lists only. It does not query domain reputation lists such as the Spamhaus DBL, and it does not support IPv6 addresses, so a domain with only AAAA records cannot be checked.
What to Do If Your IP Is Blacklisted
Treat a listing as a symptom. Look for a compromised mailbox or password, malware on a device behind the IP, an open relay, or a website form that can be abused to send mail. Once the cause is fixed, visit the operator of each list that flagged you, look the IP up on its own site to read the reason, and follow its removal steps. SpamCop entries expire automatically once reports stop; most other lists need a request.
The tool counts any answer as Listed and does not show the return code, and some operators answer with special codes that signal a query problem rather than a real listing. Always confirm on the operator’s own lookup page before you file a request. Results may also be cached for a short time, by default up to 30 minutes, so wait a little before re-checking after a delisting.
Blocklists are only part of deliverability. Make sure your SPF, DKIM and DMARC records are published and consistent with the DMARC and SPF checker, and test that the addresses on your list are well formed and have mail servers with the email validator to keep bounce rates down.
Common uses
- Finding out why email from your server bounces or goes to spam
- Checking the reputation of a new VPS or dedicated IP before running a mail server on it
- Confirming a delisting request has taken effect
- Auditing an IP before using it for newsletters or transactional email
- Investigating a suspicious IP that appears in your logs or message headers
When an unfamiliar domain shows up alongside a listed IP, the WHOIS lookup shows who registered it and when. For more network and email diagnostics, browse all security tools.
Blacklist terms explained
| Term | What it means here |
|---|---|
| DNSBL | DNS-based blocklist (or blackhole list): a list of IP addresses linked to spam or abuse that mail servers query over DNS |
| Zone | The DNS domain a blocklist answers under, such as zen.spamhaus.org or bl.spamcop.net |
| Reversed octets | The IP written backwards for the query, so 192.0.2.25 becomes 25.2.0.192 |
| Return code | The 127.0.0.x address a blocklist answers with when an IP is listed; the value usually encodes the reason |
| A record | A DNS record that maps a name to an IPv4 address; used both to resolve your domain and to query each blocklist |
| Delisting | Asking a blocklist operator to remove an IP, normally after the cause of the listing has been fixed |
Frequently Asked Questions
Enter the IPv4 address in the box and click Check Blacklists. The tool reverses the address and queries four DNS blocklists at once: Spamhaus ZEN, SpamCop, Barracuda Reputation and SORBS. Each one is reported as Listed, Clean or No answer, with a summary line at the top.
Yes. If what you type is not an IPv4 address, it is resolved with a live DNS A record lookup and the first IP returned is checked. Note that this is the address of the website, not necessarily of the mail server. To check the server that sends your email, find its IP from your MX records or a message header and enter that IP directly.
Four DNS blocklists: Spamhaus ZEN (zen.spamhaus.org), SpamCop (bl.spamcop.net), Barracuda Reputation (b.barracudacentral.org) and SORBS (dnsbl.sorbs.net). They are queried in parallel, so the whole check usually takes a moment.
It means the lookup against that blocklist failed or errored, so the tool cannot say whether the IP is listed. It is never counted as clean: if any blocklist does not answer and none list the IP, the summary warns that the result is incomplete. Running the check again a little later usually fills the gap.
A DNSBL is a DNS-based blocklist of IP addresses linked to spam or abuse. To query one, the IP octets are reversed and the list zone is appended, so 192.0.2.25 checked against Spamhaus ZEN becomes 25.2.0.192.zen.spamhaus.org. If that name returns an A record, the IP is listed; if it returns nothing, it is not.
No. Only IPv4 addresses are recognized as IPs, and anything else is treated as a domain name. An IPv6 address will not resolve, so the tool shows an error instead of a result. A domain that only has IPv6 (AAAA) records cannot be checked either.
First fix the cause, such as a compromised mailbox, an infected machine, an open relay or a form that sends spam. Then visit the operator of the list that flagged you, look up the IP on its own site to see the reason, and follow its removal process. SpamCop listings expire on their own once reports stop; most other lists need a removal request.
It can. The tool marks an IP as Listed whenever the blocklist returns any A record and does not inspect the return code. Some operators, Spamhaus in particular, return special 127.255.255.x codes to signal a query error or a blocked resolver rather than a real listing. Before you act, confirm a listing on the operator’s own lookup page.
No. It only means the IP was not found on these four lists at the time of the check. Gmail, Outlook and other providers also weigh their own reputation data, SPF, DKIM and DMARC results, sending volume and complaint rates, and there are many other blocklists this tool does not query.
No. The browser sends the IP or domain to the site’s DNS API, which performs the lookups on the server through Google Public DNS (8.8.8.8). Answers may be cached briefly, by default for up to 30 minutes, so a check repeated right after delisting can still show the old result.
Reviewed by Raja Jahangir · Last reviewed: October 7, 2026
How do you check if an IP address is blacklisted?
To check for blacklisting, enter an IPv4 address or a domain; a domain is first resolved to its A record. The reversed IP is then queried against four DNS blocklists: Spamhaus ZEN, SpamCop, Barracuda Reputation, and SORBS. A DNS answer means listed, no answer means clean, and a failed lookup is reported as unknown rather than clean.
How do you get an IP removed from a spam blacklist?
Each blocklist has its own removal process. Spamhaus, SpamCop, Barracuda, and SORBS all provide a lookup page where you enter the IP and request delisting, usually after fixing the cause, such as a compromised account or open relay. SpamCop listings expire automatically about 24 hours after the last report; the others need a manual request.