Blacklist Check
Check if an IP address or domain is listed on major DNS blacklists. All queries run in your browser via DNS over HTTPS.
What are DNS Blacklists?
DNS-based Blackhole Lists (DNSBLs), also known as Real-time Blackhole Lists (RBLs), are databases of IP addresses known to be sources of spam, malware, or other abusive email behavior. Mail servers query these lists during the SMTP connection to decide whether to accept, reject, or flag incoming messages.
Being listed on a blacklist can severely impact email deliverability. Messages from listed IPs may be rejected outright or routed to spam folders. Regular monitoring helps detect listings early so they can be resolved before causing widespread delivery failures. Pair this check with a reverse DNS lookup — missing or generic PTR records often correlate with PBL listings, and Gmail and Yahoo both ask for valid forward and reverse DNS on sending IPs. Spamhaus's Sender Guidelines also make forward-confirmed reverse DNS and a HELO hostname that resolves to the sending IP minimum requirements, and a valid-HELO, PTR and matching-A requirement is rolling out gradually from November 2026.
How DNSBL Works
The DNSBL protocol works by reversing an IP address and appending the
blacklist's zone. For example, to check IP 1.2.3.4 against
zen.spamhaus.org, the receiving server queries
4.3.2.1.zen.spamhaus.org for an A record. If an A record
exists (typically 127.0.0.x), the IP is listed. If the query
returns NXDOMAIN (no record), the IP is clean.
Through a public resolver that NXDOMAIN can be false: Spamhaus answers
Google Public DNS that way for every IP. So this tool first asks each list
about 127.0.0.2, the test entry every list must publish (RFC
5782), and only believes a list that answers it.
Common Blacklist Providers
| Provider | Focus | Description |
|---|---|---|
| Spamhaus ZEN | Comprehensive | Combined list (SBL, CSS, XBL and PBL), on by default in rspamd and SpamAssassin. It answers only a mail server's own resolver, so this tool links to Spamhaus's lookup instead of querying it. |
| SpamCop | Spam reports | User-reported spam sources and spam traps. A listing expires 24 hours after the last report. |
| Barracuda | Spam traps | Barracuda Networks' list, built from addresses that only spammers mail. |
| Mailspike | Spam waves | IPs seen in distributed spam waves, plus the worst reputation levels. |
| GBUdb Truncate | Statistics | IPs that mail filters overwhelmingly score as spam; removed automatically when the statistics change. |
If you're listed, fix the root cause before requesting delisting — the classic one is a misconfigured mail server relaying for anyone, so test your server for open-relay behavior first.
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