What the Blacklist Checker does
A DNS blocklist (DNSBL, often called a blacklist) publishes listed addresses in DNS. A receiving server reverses the sender's IP address, adds the list's zone and looks it up: 10.113.0.203.bl.spamcop.net for 203.0.113.10. An answer means listed; "no such name" means not listed. RFC 5782 describes how this works.
Enter either:
- An IPv4 address, such as the public IP of your mail server or of the service that sends your mail. We check it on every IP list below.
- An IPv6 address. IPv6 lookups use the reversed nibble format (RFC 5782 section 2.4). Only some lists publish IPv6 data: we query those, and mark the rest "No IPv6 data", which is not the same as not listed.
- A domain. We look up its MX records, resolve up to four of the mail servers to IPv4 addresses, and check each one. We also check the domain name itself on domain blocklists.
Private and reserved addresses (such as 10.x.x.x, 192.168.x.x or fc00::/7) are refused: they can't be on a public list. For a domain we check the IPv4 addresses of its mail servers; enter an IPv6 address directly to check it.
How to read the results
- Listed. The list returned one of its documented listing codes. The result shows what the code means and links to the list's removal page.
- Not listed. The list answered "no such name" for this address.
- Not tested. We couldn't get a trustworthy answer. This is never counted as clean.
- No IPv6 data. You entered an IPv6 address and this list only publishes IPv4 data. It was not tested.
Some lists carry less weight than others. UCEPROTECT Level 2 and Level 3 list whole provider networks rather than your address, and Backscatterer lists servers that send misdirected bounces, not spam. A listing there is shown as a warning, not a failure.
Why some lists show "Not tested"
Some well-known lists refuse lookups from shared public resolvers, or need registration or a personal key. When refused, they often return a special code instead of a normal answer. Spamhaus, for example, returns 127.255.255.254 for "query via public/open resolver", and some resolvers get "not listed" for everything. A careless checker reports those as listed, or as clean. We don't:
- Only each list's documented listing codes count as listed. Anything else is not tested.
- Before using a list, we look up its test entries (RFC 5782 section 5). If the always-listed test address doesn't come back listed, or the never-listed one does, we skip that list for this scan.
- Lists that refuse public resolvers are shown with a link to the operator's own lookup page.
Which lists we check
We only query lists whose operators allow free lookups like ours, including from a commercial company and through public resolvers. We checked each list's policy on the operator's site in October 2026, and we confirm each list answers its own test entries before every use.
| List | What we do | IPv6 | Removal | Operator's policy |
|---|---|---|---|---|
SpamCop (bl.spamcop.net) |
Query | No | Expires automatically once reports stop | SpamCop usage |
PSBL (psbl.surriel.com) |
Query | No | Free self-service removal | PSBL usage |
Mailspike (bl.mailspike.net) |
Query | No | Expires automatically, usually within 6 to 36 hours | Mailspike usage |
UCEPROTECT Level 1 (dnsbl-1.uceprotect.net) |
Query | No | Expires 7 days after the last spam-trap hit; paid immediate removal is optional | UCEPROTECT licence |
UCEPROTECT Level 2 and 3 (dnsbl-2, dnsbl-3) |
Query (warning only) | No | Removed automatically when the provider's network drops below the threshold; only the provider can act | Level 2, Level 3 |
Backscatterer (ips.backscatterer.org) |
Query (warning only) | No | Listed for 4 weeks after the last backscatter | Backscatterer licence |
DroneBL (dnsbl.dronebl.org) |
Query | No | Removal request, reviewed by volunteers | Using DroneBL |
Nordspam (bl.nordspam.com, dbl.nordspam.com) |
Query | Yes | Delisting form | Nordspam usage |
s5h.net (all.s5h.net) |
Query | Yes | Self-service, from the listed address | s5h.net RBL |
JustSpam (dnsbl.justspam.org) |
Query | No | Free, once the other lists have delisted you | JustSpam usage |
0spam (bl.0spam.org) |
Query | No | Free with an account | 0spam questions and answers |
Suomispam DBL (dbl.suomispam.net) |
Query (domains) | n/a | By email to the operator | Suomispam |
| Spamhaus ZEN and DBL | Link only | n/a | Spamhaus lookup | Fair use policy |
| Barracuda BRBL | Link only | n/a | Barracuda lookup | Requires registered DNS servers |
| Abusix | Link only | n/a | Abusix lookup | Requires an access key |
| SpamRATS | Link only | n/a | SpamRATS lookup | Terms: API key, no public resolvers, paid for commercial use |
| Invaluement | Link only | n/a | Invaluement lookup | Paid subscription |
| SURBL, URIBL | Link only | n/a | SURBL, URIBL | SURBL usage, URIBL |
SORBS closed in 2024, so we no longer list it. Each result row links to the list's policy and to its lookup or removal page.
Each scan makes a fixed, small number of lookups: at most four addresses and one query per list per address, plus the lists' test entries. Results are cached for five minutes.
Common problems and fixes
Listed on one small list. Not every list carries the same weight. Some lists, including UCEPROTECT, sell faster removal; you rarely need to pay, because their listings expire on their own once the cause is fixed. Read the list's listing reason, fix the cause, and request removal. Some, like SpamCop and Mailspike, expire entries automatically.
Listed after a compromised mailbox. Reset the password, turn on multi-factor authentication, check for forwarding rules the attacker added, and only then ask for removal. Our guide why did this email land in spam covers the other signals receivers use.
Shared hosting or a shared relay. If you send through a shared server, another customer's spam can get the IP listed. Ask your provider to fix it, or move to a sending service with dedicated reputation management.
Missing reverse DNS. Some lists and many receivers distrust addresses without a PTR record. Check yours with the Reverse DNS (PTR) Lookup.
Limitations
- The big mailbox providers (Gmail, Microsoft, Yahoo) mostly use their own reputation data. A clean result here doesn't mean they trust your server.
- Listings change hourly. The result is a snapshot from the time shown.
- For a domain, we check its inbound mail servers. Your outgoing mail may leave from other servers, such as your mail provider's or a newsletter service's.
- A listing is usually a symptom. Removal without fixing the cause tends to end in a new listing.
Related
Check your sending setup with the Email Health Check, or read about backscatter and bounce spam, a common reason for listings.
Frequently asked questions
What is an email blacklist?
An email blacklist, or DNS blocklist (DNSBL), is a list of IP addresses or domains seen sending spam. Receiving mail servers look up the sending IP in DNS while mail arrives and may reject or junk messages from listed addresses.
Why does it say Spamhaus was not tested?
Spamhaus doesn't answer lookups made through public DNS resolvers, which is how this tool queries, and its free service is for non-commercial use. Rather than guess, we mark it not tested and link to Spamhaus's own lookup page, where you can check for free.
Can the Blacklist Checker test an IPv6 address?
Yes. IPv6 addresses are looked up in the reversed nibble format on the lists that publish IPv6 data (currently Nordspam and s5h.net). Lists that publish only IPv4 data are shown as "No IPv6 data": not tested, never clean.
Do I have to pay to get off a blocklist?
Usually not. Most lists remove entries for free, and some, such as UCEPROTECT, expire listings automatically once the spam stops and only charge for faster removal. Fix the cause first; paying without fixing it tends to end in a new listing.
I'm listed. How do I get removed?
Fix the cause first: a compromised mailbox, an infected computer, an open relay or a website form that sends mail. Then use the removal link for each list. Many lists expire entries automatically once the spam stops.
Should I check my domain or my IP address?
Check the IP address of the server that sends your mail, because that's what receivers look up. A domain check covers the servers in your MX records, which receive your mail and are often different from the ones that send it.
Does a clean result mean my mail will be delivered?
No. It means the lists we could query don't list that address today. Large mailbox providers such as Gmail and Microsoft use their own reputation data, which no public lookup can show.
Related guides
How to get your domain or IP removed from an email blacklist
How to check if your mail server IP or domain is on a DNS blocklist, find the real cause, and request removal from Spamhaus, SpamCop, Barracuda and Microsoft.
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