IP & Domain Blacklist Checker
Check your IP or domain against 12 major spam blacklists simultaneously. Instant DNSBL lookup — see if you're listed and how to get removed.
How DNS Blacklists Affect Email Deliverability
Email blacklisting is one of the most common and disruptive problems for businesses that rely on email communication. When your IP or domain appears on a DNSBL, receiving mail servers silently reject your messages or route them to spam — you may not even know it's happening until customers report not receiving your emails.
The blacklists that matter most:
- Spamhaus ZEN: The most widely used blacklist, consulted by the majority of mail servers worldwide. A Spamhaus listing will block delivery to most major business email providers. If you're only listed here, this is the one to prioritize.
- Barracuda: Used heavily by enterprise mail filtering appliances. Common in corporate environments with Barracuda Email Security Gateways.
- SpamCop: Based on user-submitted spam reports. Listings are time-limited — they expire automatically 24–48 hours after the last report, provided no new spam is sent.
- SORBS: A collection of sub-zones covering different types of abuse — spam sources, open proxies, dynamic IP ranges, and web form spammers.
- UCEProtect L1: Lists individual IPs that have sent spam. Levels 2 and 3 are broader (listing entire IP ranges and ASNs) but L1 is the most targeted and most commonly acted on.
Reading the blacklist report
Each row in the output pairs one DNSBL with a verdict. A "listed" result means the query returned an A record (often 127.0.0.2 through127.0.0.11, where the final octet encodes the listing reason). A "clean" result means the DNS query returned NXDOMAIN on that specific zone.
- Spamhaus ZEN listed: the single most damaging result — treat as urgent, since most business mail servers consult ZEN directly.
- Spamhaus PBL only:your IP is inside a range the ISP flagged as "end-user / dynamic"; legitimate mail should go through your provider's smart host, not direct from this IP.
- SORBS DUHL or SPAM: often a shared-hosting false positive where a neighbor on the same /24 sent abuse.
- SpamCop listed: listings decay after 24–48 hours with no new reports — if the cause is fixed, re-check the next day.
Common issues and fixes
- Spamhaus PBL listing on a static IP: request that your ISP remove the range from the PBL, or relay outbound mail through an authenticated submission service on port 587.
- SORBS shared-hosting false positive: ask the host to migrate you to a dedicated IP, then submit a delisting request with evidence of SPF/DKIM alignment.
- Relisted within hours of removal: the root cause is still active — audit for compromised mailboxes, abused contact forms, or malware on CMS installs before retrying delisting.
- Listed with no outbound mail: check whether your IP was previously assigned to a spammer; providers like DigitalOcean and Hetzner rotate IPs and listings can carry over.
- UCEProtect L2/L3 listing you cannot clear: L2 and L3 list whole ranges and ASNs; escalation requires your hosting provider, not you.
What to do next
Once you know which RBLs flagged you, fix deliverability fundamentals before requesting removal: publish SPF, enable DKIM signing, and set DMARC to at leastp=none with aggregate reports. Then submit delisting on the major lists (Spamhaus, Barracuda, SORBS) and monitor for re-listing over the next week.
For continuous monitoring, FlashMon.app tracks changes automatically and alerts you the moment something breaks.
Monitor blacklists automatically
Get instant alerts the moment your IP or domain appears on any blacklist — catch deliverability problems before they affect your business.
Frequently Asked Questions
A DNS-based blackhole list (DNSBL), also called a real-time blackhole list (RBL), is a list of IP addresses known to send spam or host malicious activity, published as a DNS zone. Mail servers query these lists in real time for every incoming connection: to check whether 1.2.3.4 is listed on zen.spamhaus.org, the mail server queries 4.3.2.1.zen.spamhaus.org — if the query returns an A record, the IP is listed and mail from it is likely rejected or flagged. If the query returns NXDOMAIN (no such domain), the IP is clean. This tool automates that lookup across 12 major blacklists simultaneously.
Common reasons for blacklisting include: (1) Your server sent spam — either directly or because a compromised account or application was abused. (2) Your IP was previously owned by a spammer and the listing carried over. (3) Your server is an open relay or open proxy, allowing anyone to route traffic through it. (4) Malware on a hosted website sent outbound spam or phishing emails. (5) Your sending volume or patterns triggered automated spam detection. Always check the specific blacklist's website for the reason — most provide a lookup tool that shows why the IP was listed and when the listing expires.
First, fix the root cause — otherwise the IP will be relisted within hours of removal. Then: Spamhaus (zen.spamhaus.org) offers a self-service removal at spamhaus.org/removal after the problem is fixed. Barracuda (b.barracudacentral.org) has a form at barracudacentral.org/lookups. SpamCop (bl.spamcop.net) listings expire automatically after the spam reports age out — usually 24–48 hours after the last complaint. SORBS (dnsbl.sorbs.net) requires submitting a removal request through their web form. Most listings expire automatically within days to weeks if no new complaints are received. Re-run this checker after 24 hours to confirm removal has propagated.
For most blacklists, the impact is primarily on email deliverability — receiving mail servers check these lists before accepting connections, so a blacklisted IP may have email bounced or sent to spam. Your website being served over HTTPS on the same IP is typically unaffected since web browsers don't consult DNSBLs. However, some enterprise firewalls and security appliances do block web traffic from blacklisted IPs. Google and other search engines do maintain their own separate lists for web spam that aren't covered here — if you're seeing search ranking drops, check Google Search Console for manual actions instead.
Several scenarios can cause listings without intentional spam: (1) A shared hosting environment where your IP is shared with other customers, one of whom was a spammer. (2) A WordPress or other CMS site that was compromised and used to send phishing emails. (3) A contact form being abused to relay spam. (4) An email account on your server was compromised via a weak password. (5) The IP was previously owned by a spammer before you were assigned it. Check your mail server logs for unusual outbound activity, scan your web applications for malware, and review all email accounts for unauthorized activity. Many hosting providers have server-level logs that can help identify the source.
For businesses that depend on email delivery, checking weekly is a good baseline. For high-volume email senders, checking daily or setting up automated monitoring is recommended — a blacklisting that goes unnoticed for days can cause significant email bounce rates and missed communications. FlashMon can monitor your IP or domain against blacklists continuously and alert you immediately if a listing appears, so you can take action before it impacts your operations.