Blacklist Checker
Check a domain or IP against the major email blacklists.
A DNS blocklist is a list of addresses published as DNS records. To check one, a mail server reverses the IP, appends the list’s zone, and looks it up — an answer means listed, an NXDOMAIN means not. That design is why the check costs nothing and why it happens on essentially every message the internet delivers.
Listings are not equal. A Spamhaus entry affects delivery across a large share of the internet; several of the smaller lists are consulted by almost nobody, and a few have reputations for listing aggressively and delisting slowly. Read a listing as a signal to investigate rather than a verdict, and weigh it by who actually uses the list.
The order of operations for a real listing matters. Find and stop the cause first — a compromised account, an open relay, a script sending to a stale list — then request delisting. Asking for removal while the behaviour continues gets the request refused and can lengthen the listing.
What this tool does
A dozen lists at once
Spamhaus, Barracuda, SpamCop, SORBS and others queried in parallel, with each result shown separately.
Domains and IPs
A domain is resolved first and its address checked, since IP lists are what receiving mail servers consult.
Reasons where given
Lists that publish a reason code have it shown, which is usually the fastest route to understanding a listing.
Plain DNS
DNSBLs are queried over DNS exactly as a mail server would. No API keys, no accounts, nothing submitted anywhere.
Frequently asked questions
What is a DNSBL?
A DNS-based blocklist. Listed addresses are published as DNS records under a zone, so checking one is a normal DNS query rather than an API call: the address is reversed and looked up under the list's domain, and an answer means it is listed. Mail servers use exactly this mechanism, thousands of times a day.
Why is my IP blacklisted?
The usual causes are a compromised machine or account sending spam, a misconfigured mail server acting as an open relay, a shared or recycled IP carrying someone else's history, or a spam trap address being mailed. Most lists tell you which when you look up the address on their own site.
How do I get delisted?
Fix the cause first, because a delisting request on a still-sending IP is refused and can extend the listing. Then use the list operator's removal form. Many lists expire entries automatically once the behaviour stops, so for a one-off incident waiting is often the fastest route.
Which blacklists actually matter?
Spamhaus is the one with real reach — a listing there affects delivery to a large share of the internet. Barracuda and SpamCop carry weight with particular providers. Many smaller lists are used by almost nobody, so a listing on one is worth understanding but rarely worth panicking about.
Does a clean result mean my mail will be delivered?
No. Blacklists are one input among many. Gmail, Outlook and other large providers run their own reputation systems that no public list reflects, and they weigh authentication, engagement and complaint rates heavily. A clean DNSBL result rules out one specific problem, not delivery problems in general.
Should I check my domain or my sending IP?
Both, because they are listed separately. Domain lists cover the domains appearing in message content and headers; IP lists cover the machine that made the connection. If you send through a provider, their sending IPs are what receiving servers check, so your own server's IP may be irrelevant.
Is anything sent to the blacklist operators?
Only a DNS query, which is how the lists are designed to be used. There is no account, no API key and no submission of your address to anyone — the query looks identical to the ones mail servers make constantly.
Monitor it, don't just check it
One-off checks catch what is broken today. CertNotify watches your certificates, domains, DNS and code continuously and tells you before something breaks.