Find out whether a mail server's IPv4 address is on a spam blocklist. The checker queries 21 public DNSBLs (Spamhaus, SpamCop, Barracuda, UCEPROTECT and more) in parallel and shows listed, clean or unknown for each one, with the return code and a link to request removal.
Last updated:
127.0.0.2 is the standard test address every DNSBL lists on purpose, so it shows what a listing looks like. Enter your own mail server's IP to check it.
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Blacklist
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How to use the IP Blacklist Checker
Enter an IPv4 address such as your mail server's outgoing IP, or a host name like mail.example.com.
Click Check Blacklists. Each list is queried with the reversed IP address over DNS-over-HTTPS.
Read the summary: the big number is how many lists currently list the IP.
Open a listed row's removal link to see why it is listed and how to request delisting, after you fix the cause.
Copy or download the results to share with your host or IT team.
Spamhaus ZEN return codes
Answer
Zone
Meaning
127.0.0.2
SBL
Spam source or spam operation verified by Spamhaus staff
127.0.0.3
SBL CSS
Snowshoe spam: low-volume spam spread across many IPs
127.0.0.4 to .7
XBL
Host infected by malware or abused as a proxy (includes the former CBL)
127.0.0.9
SBL DROP
Hijacked or criminal network range
127.0.0.10, .11
PBL
Policy listing: end-user IP that should not send mail directly
127.255.255.252 to .255
Error
Query refused: public resolver, rate limit or typo in the zone name
How the lookup is built
The four octets of the IP address are reversed and the blocklist zone is appended. For 198.51.100.7 and SpamCop the query is 7.100.51.198.bl.spamcop.net, record type A. Reversing puts the most specific part first, the same way reverse DNS works under in-addr.arpa, which lets operators list whole ranges with wildcards. A TXT query for the same name often returns a short reason and a link.
Give the IP a reverse DNS (PTR) name that resolves back to the same IP. Check it with Reverse DNS Lookup.
Never send to purchased or scraped lists; they are full of spam traps that feed these blocklists.
Rate-limit outgoing mail and require authentication so a single stolen password cannot send thousands of messages.
Remove bounced addresses promptly and honour unsubscribes within two days.
Frequently asked questions
How does an IP blacklist check work?
DNS blocklists (DNSBLs) publish their data in DNS. To check 203.0.113.25 on zen.spamhaus.org you look up 25.113.0.203.zen.spamhaus.org. If the name exists and returns an address in 127.0.0.0/8, the IP is listed and the returned code explains why. If the name does not exist (NXDOMAIN), the IP is not listed.
Why does 127.0.0.2 show as listed everywhere?
By convention every DNSBL lists 127.0.0.2 permanently as a test entry, so you can confirm the list is answering. It is the default example here so you can see what a listing looks like. Enter your own IP to check it.
Why do some lists show Unknown?
Some operators, notably Spamhaus, refuse queries that come through large public resolvers such as Cloudflare and Google and answer with a special 127.255.255.x code instead. Others may be slow or offline. The tool reports these as unknown instead of clean; use the list's own lookup page to confirm.
What is the Spamhaus PBL?
The Policy Block List contains IP ranges that ISPs say should not send email directly, such as home broadband and mobile addresses. It is not a sign of spam. Mail servers should send from a static IP with matching reverse DNS, or relay through a provider.
How do I get removed from a blacklist?
First fix the cause: a compromised account or device, an open relay, a hacked web form or sending to old purchased lists. Then use the list's removal page. Many lists, such as SpamCop and PSBL, expire listings automatically once the spam stops; UCEPROTECT levels 2 and 3 cover whole networks and are cleared by the network owner fixing abuse.
Does being listed mean my email will bounce?
It depends on which list. Major providers rely on a few lists such as Spamhaus, and a listing there often causes rejections. Smaller lists are used by fewer servers, so a listing may affect only some recipients. Fix any listing, but prioritise the widely used ones.
Is my IP address sent to FreeToolCabin?
No. Your browser sends the DNS queries directly to Cloudflare's or Google's public DNS-over-HTTPS resolver, which forwards them to each blocklist. FreeToolCabin has no server involved and stores nothing.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.