Blacklist (DNSBL) check: is your IP or domain listed?
How does this check work, and what does the result tell you?
Yes: a DNSBL lookup is just a DNS query, so you can check for free without any AdminKit account by reversing your mail server's IP octets, appending a blocklist zone, and querying for an A record; any answer in the 127.0.0.x range means a listing. For many mail servers or a stubborn listing, talk to the Netbase team.
Part of the Email authentication cluster — more tools, guides and terms on email authentication.
Your current IP, or a domain you enter, checked against several major public DNSBLs in one pass.
- Which specific lists you are on, and why — each has its own cause and delisting process
- A direct link and plain-language steps to request delisting from each list found
- Need blocklist monitoring for your mail servers? Talk to our team about a custom setup built by Netbase
Next step
Check your current IP, or look up a domain's registration.
Keep this result
Copy a link to this check so you can share it or run it again later. Want a heads-up when this result changes? Talk to our team and we'll set it up for you.
How it works and limits
A DNSBL (DNS-based blocklist) lists IP addresses and domains associated with spam, malware or abuse. A listing on a widely used DNSBL causes many mail servers to silently reject or quarantine your mail, and in severe cases browsers or security software may warn visitors away from a listed domain.
What should a blacklist check cover?
- Your current public IP, or a domain you send mail from, against several major public DNSBLs.
- Which specific lists it is on, since each has its own cause (spam source, open relay, compromised host, malware C2) and delisting process.
- The list-specific delisting steps for each listing you find.
Why run the lookup from your own resolver?
Blocklist operators limit query volume, and Spamhaus refuses queries that arrive through large public resolvers, so a lookup
from your own network’s resolver gives the most reliable answer. An answer of 127.255.255.254 from Spamhaus is an error code for “query via public/open resolver”,
not a listing. Making a fresh DNS query per DNSBL for many
addresses can also trip the lists’ own abuse protections, so check their usage terms before scripting it.
How do I check an IP manually?
A DNSBL lookup is itself just a DNS query: reverse the IP’s octets, append the DNSBL zone, and query for an A record.
For example, to check 203.0.113.5 against Spamhaus ZEN:
dig +short 5.113.0.203.zen.spamhaus.orgAny A record in the 127.0.0.x range means a listing (the exact address encodes the reason); no answer means not
listed on that zone. Repeat against other DNSBL zones you care about — see Spamhaus’s usage terms for query-volume
limits before scripting this against many addresses.
If a lookup comes back listed, see the list-specific removal procedure: how to get delisted from Spamhaus or how to get delisted from the Barracuda Reputation Block List. See also the glossary entry for DNSBL, and how AdminKit’s free checks compare in AdminKit vs MxToolbox. Sending mail from many servers, or stuck on a listing that keeps coming back? Talk to our team about a Netbase mail-reputation review.
Frequently asked questions
How does this page check a blacklist?
It walks you through the lookup by hand, because a DNSBL query is a plain DNS query you can run yourself. Blocklist operators set query-volume limits and usage terms, so the check runs best from your own resolver: Spamhaus alone combines four separate blocklists (SBL, CSS, XBL and PBL) into one zone it describes as "the combination of all Spamhaus' free IP-based DNSBLs into one single powerful and comprehensive blocklist" (Spamhaus, ZEN DNSBL).
What can I check right now?
Run one dig command against a public DNSBL zone such as zen.spamhaus.org; any answer in the 127.0.0.x range means a listing, per Spamhaus's own return-code documentation — see the linked guide for the full method and other zones.
Which DNSBLs are worth checking?
A handful of widely used, mail-server-trusted zones, starting with Spamhaus's ZEN, which alone combines four separate blocklists (SBL, CSS, XBL and PBL) covering spam sources, open relays, compromised hosts and malware C2 — not every DNSBL that exists, since many are low-traffic or unmaintained.
How do I read a listing result?
By the specific list name it was found on and Spamhaus's own return code for that cause — for example 127.0.0.2 for its Spamhaus Block List (direct spam sources) versus 127.0.0.4 for its Exploits Block List (botnet-infected hosts) — not a generic 'blocked' badge, because each code has a different delisting process.
Can Netbase monitor our mail servers for listings?
Yes, as a custom engagement. The Netbase team can check your mail servers and office IPs against the major blocklists, trace the cause of a listing and work through delisting with you. Talk to our team at /contact/ with the IPs or domains you send mail from.