What a DNSBL is
A DNS-based blocklist is a database of IP addresses, published through DNS so that mail servers and security tools can query it in milliseconds. To check an address, a client reverses its octets, adds the list's domain name and sends a DNS query. A positive answer means the address is listed. This tool does exactly that for each of the 10 lists, from your browser through a server-side check, so what you see matches what a receiving mail server would find.
Reading the result
- Not listed: the list does not include the address.
- Listed: the address is currently flagged. The list's own site explains why and how to ask for removal.
- Unavailable: the list could not be queried, for example because of a resolver limit. Run the check again later instead of assuming either way.
Lists have different standards. Spamhaus ZEN combines several lists and is widely used by mail providers, so a ZEN listing is usually the one to fix first. Others such as UCEPROTECT L1 or SORBS use their own criteria, and some mail servers ignore them. The number of listings and the identity of the lists together give the picture.
Why proxy users should check
Recycled addresses carry the history of earlier users. If you send mail from a proxy or server, or if a site reads blocklists to treat a connection with suspicion, a listing can lead to rejections or more challenge pages. For rotating residential proxies, test a few exits instead of one. For a dedicated address such as a static datacenter IP, check on delivery and re-check before using it for mail. The IP reputation check turns the same 10 results into a 0-100 score (100 minus 20 per listing).
How to fix a listing
- Identify the cause: malware, an open relay, a misconfigured mail server or a shared neighbor.
- Fix it first. Delisting before the cause is gone often results in relisting.
- Follow the removal process on the list's website; most are self-service.
- If the address belongs to a proxy provider, ask for a different IP instead; for sticky sessions, start a new session ID.
- Check IPv6 separately; this tool checks IPv4 only.
Need a different IP or location?
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Frequently asked questions
Ten public DNSBLs: Spamhaus ZEN, SpamCop, Barracuda, SORBS, PSBL, UCEPROTECT L1, s5h.net, DroneBL, Mailspike and NiX Spam.
No. It supports IPv4 only, because these lists are queried by IPv4 address.
The list could not be reached or answered with an error, so the tool does not report it as clean or listed. Try again later.
Remove the cause first, such as malware or an open relay, then use the removal process of each list that includes your IP. Delisting before the fix usually leads to relisting.
Yes. Addresses are reused, so an earlier user's behavior can leave a listing. Request a different exit and compare with the IP reputation score.