Check a mail server IP against spam blocklists, and see which lists a browser cannot check
Runs in your browser. Only the lookup you start is sent to cloudflare-dns.com or dns.google; nothing else leaves your device. Updated on 24 Oct 2026.A blacklist checker looks a mail server's IPv4 address up in DNS blocklists: the address is reversed, joined to the list's zone and asked for an A record, and an answer in 127.0.0.x means listed. This page checks 5 lists that allow it and explains why Spamhaus cannot be checked from a browser.
Type the address in IPv4 address of the sending mail server, such as 192.0.2.10.
Press Check lists to ask each blocklist, each with its own test entry checked too.
Read the headline for how many of the lists checked show the address as listed.
Read the Result and What it said columns, and open Delisting under Links for a list that has it.
Read Not checked from a browser for lists this page cannot query, such as Spamhaus.
Enter the public IPv4 address your mail server sends from, and the page asks five DNS blocklists whether they list it: SpamCop, the Passive Spam Block List (PSBL) and three 0spam lists. Each result shows listed, not listed or could not check, the reason text the list publishes, and links to its delisting page and its usage policy.
The set is small on purpose. A browser can only ask public resolvers such as Cloudflare and Google, and several big lists refuse those. Spamhaus answers them with a "query refused" code, 127.255.255.254, and through Google with a fake "does not exist" that other sites show as "not listed". Barracuda only answers resolvers registered with it. SURBL and URIBL block public resolvers too, UCEPROTECT has its own rules for automated lookups, and SORBS closed in June 2024. Those lists are named on the page with a link to check each one on its own site, and never shown as clean.
Every answer is tested before it is trusted. RFC 5782 requires every list to list the test address 127.0.0.2 and never 127.0.0.1. Alongside your address, each list is asked about 127.0.0.2; if that does not come back listed, a "not listed" for your address is reported as "could not check" instead. Answers of 127.0.0.1 or 127.255.255.x are read as refusals, and an answer outside 127.0.0.0/8 as a resolver rewriting DNS.
What it does not do. It checks IPv4 addresses only, not domains or IPv6. It cannot check Spamhaus, which most large providers use; do that at check.spamhaus.org. Private, loopback and documentation addresses are explained rather than sent, because no public list can hold them.
The address, reversed and joined to each list's name, goes to the resolver you choose, which asks the lists. The lists see the resolver, not you.
Enter the public IPv4 address of your mail server and press Check lists. Each list shows listed, not listed or could not check. To find the address, open a message you sent in the recipient's mailbox, view the original headers, and take the first public IP in the Received lines.
Spamhaus refuses queries arriving through public resolvers such as Cloudflare and Google, because it cannot tell how many lookups each user makes. A browser can only use those resolvers, so Spamhaus answers with a refusal code or a fake not-found. Use Spamhaus's own checker at check.spamhaus.org for an honest answer.
An A record answer inside 127.0.0.0/8 means the address is listed, and the last number says why on lists that use several codes. RFC 5782 also makes 127.0.0.2 the test entry every IPv4 list must list, so checking that address shows what a listing looks like on each list.
First stop what caused it: a compromised account, an open relay, or mail to bought lists. Then use the list's own page, linked beside each result. SpamCop delists automatically about 24 hours after reports stop, PSBL lets anyone remove an address at once, and 0spam removals need a free account.
No. Proofpoint closed SORBS on 5 June 2024 and its zones no longer hold reputation data. A checker that still reports SORBS results is reporting nothing, so SORBS is listed on this page as closed rather than queried.
The address, with its four numbers reversed and joined to each list's zone name, is sent to the resolver you pick, Cloudflare or Google, which then asks the lists. The lists see a query from the resolver, not from you. Nothing else is sent and nothing is stored.
Still stuck? Ask about Blacklist Checker and anybody who knows can answer. No account needed.
Same job, other tools: Find the Sender IP of an Email – Paste the headers of an email to find the IP address of the server that sent it.
On the related tools: SPF Record Generator – Write an SPF record for your mail providers and see how many lookups it uses · DMARC Record Generator – Build a DMARC record step by step, from p=none reporting to p=reject.