Enter an IPv4 address to check it against more than 20 public email DNS blacklists (DNSBLs) including SpamCop, Barracuda, UCEPROTECT, PSBL, Mailspike, and DroneBL, grouped by importance. It is free, runs instantly in your browser over DNS-over-HTTPS, needs no signup, and stores nothing.
A DNS blacklist, also called a DNSBL or RBL, is a published list of IP addresses with a history of sending spam or abusive traffic. Mail servers query these lists in real time over DNS, and if your sending IP is listed, the receiving server can defer, junk, or outright reject your message. Lists differ in how aggressive they are and how they decide what to list: some react to spam-trap hits and complaints, others escalate to whole subnets or networks. This tool queries each list for the IP you enter and reports back which ones return a listing. Staying off the major DNSBLs is a core part of email deliverability, alongside SPF, DKIM, and DMARC.
A DNSBL answers each query with an address in the 127.0.0.0/8 range when an IP is listed, and with no record when it is clean. So a 'listed' result means the list operator currently flags your IP, and 'not listed' means it does not appear on that list right now. Some operators reply to public-resolver queries with a 127.0.0.1 or 127.255.x code that the tool shows as 'no answer' (a blocked query), not a listing, so only 127.0.0.2 and higher count as a real listing.
This tool checks more than 20 public-resolver-friendly lists, the same providers reputable commercial checkers run, grouped by importance: SpamCop, Barracuda, Mailspike, DroneBL, PSBL, GBUdb Truncate, UCEPROTECT Levels 1 to 3, InterServer, 0Spam, Scientific Spam, Backscatterer, NordSpam, and more regional and specialized lists. Each operator sets its own listing rules, so being on one does not always mean you are on the others. Every list is verified to leave known-clean IPs unlisted, so a clean IP is never falsely flagged.
Spamhaus ZEN blocks lookups sent through public DNS resolvers (such as Google and Cloudflare), so a browser-based check can never get a trustworthy verdict from it. Rather than show a meaningless row, the tool links it below the results. Check Spamhaus directly at check.spamhaus.org to be sure your IP is clean there too.
Level 1 lists an individual IP, Level 2 escalates to the surrounding subnet or allocation, and Level 3 lists an entire network (ASN). A Level 2 or 3 hit often reflects a noisy neighbor on shared infrastructure, not your own IP behaving badly.
Alongside the blacklists, the tool checks the IP's reverse DNS. A PTR record that resolves back to the same IP (forward-confirmed, or FCrDNS) is expected by Gmail, Yahoo, and Microsoft. A missing PTR is a common reason mail from an otherwise clean IP is rejected or filtered.
Levels 2 and 3 do not list your specific IP for your own behavior. They flag the wider subnet or the whole network (ASN) because of other senders on it. Most receivers weight these lists lightly, so confirm whether your mail is actually being blocked before reacting, and raise it with your hosting provider or ESP, who owns the network range.
On a shared sending IP, one bad sender can get the address listed and hurt everyone on it. You usually cannot fix this alone: report it to your email provider or host so they can remediate and request delisting. If listings keep recurring, move to a dedicated IP and warm it up gradually.
A spike in spam, an open relay, a hacked account, or a malware-infected machine on your network can trigger a listing fast. Find and shut down the source first, rotate credentials, and patch the cause. Requesting delisting before the problem is fixed usually gets the IP relisted within hours.
Listings clear in different ways. SpamCop expires on its own once the abuse stops, often within about a day. UCEPROTECT Level 1 also auto-expires for free, but only after the IP has been clean for seven days. PSBL auto-expires too, though that can take two to three weeks, so use its instant self-service removal form once you have fixed the cause. Barracuda and Mailspike do not auto-clear quickly: submit a removal request through the operator's form after you have resolved the issue.
