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DNS Blacklist Check
dns-blacklist-checkCheck whether a domain or IP appears on known blocklists used by mail and security systems.
Enter a target and run the tool.
Results
| Type | TTL | Value |
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About DNS Blacklist Check
DNS-based blacklists — called DNSBLs or RBLs (Real-time Blackhole Lists) — are distributed reputation databases that mail servers and security gateways query in real time before accepting traffic from a given IP or domain. If your sending IP appears in Spamhaus, Barracuda, SORBS, or SpamCop, the receiving mail server can reject or defer your delivery — usually with an SMTP 550 error that names the blacklist responsible. Many sending teams discover a listing only after delivery rates drop or after a bounce report includes a URL pointing to a blacklist entry.
A blacklist check resolves your IP or domain against dozens of reputation feeds at once and shows which, if any, are listing you and under which category. Once you know which lists are involved, each publishes its own removal procedure. Running the check after completing the removal process confirms the delisting before you resume sending.
How DNS blacklists work
DNSBL lookups are DNS queries. For IP-based checks, the IP address is reversed and prepended to the blacklist's query domain. Checking 1.2.3.4 against zen.spamhaus.org queries 4.3.2.1.zen.spamhaus.org. If the query returns an A record rather than NXDOMAIN, the IP is listed. The returned address's last octet encodes the listing reason — for Spamhaus, different return values distinguish between SBL (known spam sources), XBL (exploited systems), and PBL (ISP-designated non-sending ranges).
The most impactful blacklists for email deliverability are Spamhaus and Barracuda. Gmail, Outlook, and Yahoo weight these heavily. A listing in a smaller community-operated DNSBL may have limited practical effect on deliverability, while a Spamhaus SBL listing requires immediate investigation and action.
Why this matters beyond email
IP and domain reputation affects more than inbox placement. Security gateways, web application firewalls, and DNS-level filtering services reference DNSBL data to block connections from known malicious sources. An IP listed in a URL or domain blacklist (such as Spamhaus DBL or SURBL) affects whether web requests from that IP are accepted, whether browser extensions flag the domain as unsafe, and whether some corporate proxies allow outbound connections to the domain.
The AT USE workflow
Enter the IP address or domain you want to check. The tool routes your query to a multi-engine lookup that covers the major commercial and community-operated blacklists. Results open in a new tab and show a line-by-line status for each blacklist — listed or clean — plus the listing reason where the blacklist publishes one. For any listing, follow the link to that blacklist's removal procedure.
Common use cases
- Diagnosing why outbound email is bouncing — A developer's application sends transactional emails — order confirmations, password resets — and starts receiving SMTP 550 bounces. The error includes a URL pointing to a Spamhaus lookup. Entering the sending IP into the blacklist check confirms a Spamhaus PBL listing. PBL lists IP ranges designated by ISPs as non-sending — the fix is routing outbound mail through an SMTP relay service rather than sending directly from the application server's IP.
- Verifying a new sending IP before a campaign launch — A growth team at a SaaS company is launching its first email marketing campaign and wants to confirm clean IP reputation before sending. They check both the outbound IP addresses of their ESP and the sending domain. One IP has a Barracuda listing from a previous tenant of that IP range. They request a different IP from the ESP, re-check it, and confirm clean status before the campaign sends.
- Post-incident reputation audit after an account compromise — A security team discovers a compromised user account was used to send spam for 36 hours before being locked. After containing the breach, they run a blacklist check on all outbound mail server IPs. Three listings appear — SORBS SMTP and SpamCop. They submit delisting requests, fix the underlying account security issue, and re-check after 48 hours to confirm all three listings are removed before resuming normal mail sending.
- Monitoring a shared hosting environment for noisy-neighbor damage — A developer runs transactional mail from a VPS provider where multiple tenants share the same IP block. Periodically checking the sending IP confirms whether neighboring tenants have generated spam complaints that affected shared IP reputation. When a Spamhaus CBL listing appears on the shared IP, the developer requests a dedicated sending IP from the provider rather than waiting for reputation recovery on the shared block.
- Auditing a domain acquired through a company acquisition — A development team inherits a domain from a company acquisition and needs to understand its reputation before using it for email or services. A blacklist check against the domain and its known mail server IPs reveals an existing SORBS listing from the prior owner's operations. The team resolves the listing before migrating any traffic to the domain.
How to use this tool
- Enter the IP address or domain you want to check.
- Click "Open Blacklist Check" to launch the multi-engine reputation lookup.
- Review which blocklists, if any, have the value listed.
- For each listing, follow the blocklist's published removal procedure.
Frequently asked questions
My IP is listed but I haven't sent spam. Why?
Several non-spam reasons exist. Spamhaus PBL lists IP ranges that ISPs designate as non-sending — this is a policy designation, not a spam detection. If your IP is on a residential or cloud-provider range not intended for outbound mail, PBL listings appear regardless of sending behavior. Spamhaus CBL lists IPs with evidence of botnet or malware activity — a compromised device on the network, not necessarily intentional spam. Barracuda sometimes lists IPs from newly allocated blocks that were previously associated with abusive senders. The specific listing's reason code tells you which category applies.
How long does delisting take?
It varies by blacklist. SpamCop listings expire automatically after 24–48 hours if no new complaints arrive against the IP. Spamhaus SBL and XBL require a manual request and typically resolve within hours to a few days after the underlying issue is confirmed fixed. Barracuda delisting is usually automatic within 12–24 hours after a form submission. SORBS is slower and sometimes requires additional documentation. Run the check again after the expected window to confirm removal.
Will running this check trigger any new listings?
No. A DNSBL lookup is a standard DNS query — read-only and anonymous. Querying a blacklist does not add your IP to it. The lookup shows what's already there, nothing more.
Should I check the IP, the domain, or both?
Both, when possible. IP-level reputation drives the initial SMTP connection acceptance or rejection. Domain-level reputation (checked via Spamhaus DBL and URIBL) increasingly affects spam folder placement at Gmail and Microsoft 365. A sending IP that's clean but a domain that's listed in a URL blacklist can still result in spam-folder delivery even when the connection is accepted.
What is the difference between SBL, XBL, and PBL in Spamhaus?
SBL (Spam Block List) lists IP addresses directly involved in spam operations — known spam sources and infrastructure. XBL (Exploits Block List) lists IPs hosting exploited systems, open proxies, and malware command-and-control servers. PBL (Policy Block List) lists IP ranges designated by ISPs as not authorized for direct mail delivery — mostly residential and dynamic IP ranges. An SBL or XBL listing means the IP has been used for abuse. A PBL listing means the IP range isn't supposed to send mail directly and requires routing through an SMTP relay.
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