IP Address / Domain Blacklist (DNSBL) Checker

Enter an IP address or domain to check it against major DNSBLs (blacklists) such as Spamhaus, SORBS, Barracuda, and SpamCop all at once to see if it's been flagged as a spam source.

Tips

  • If your emails aren't reaching recipients or keep landing in spam folders, start by checking here whether your sending IP address is listed on a blacklist.
  • Enter a domain and this tool automatically resolves its A record (IPv4 address) first, then queries each blacklist — there's no need to look up the IP yourself in advance.
  • If you send mail from a shared server or shared IP address, you can end up listed as collateral damage from another user's spam activity on the same IP.
  • If a listing turns up, check the official site for that blacklist (linked from the results) for its delisting procedure. Most providers let you request removal for free.
  • DNSBL data isn't always perfectly up to date, so it's best to check across multiple blacklists rather than basing a decision on a single result.

Frequently asked questions

Mail servers that consult that blacklist may mark messages from your sending IP address as spam, or reject them outright. Spamhaus ZEN in particular is checked by a huge number of mail providers, so a listing there can have a significant impact.

Each blacklist operator provides a delisting request form on its official site. Most are free — once you confirm you've stopped sending spam or fixed the underlying cause, removal typically happens within a few hours to a few days.

On shared servers or dynamically assigned IP addresses, a listing can stem from spam sent earlier by a different user who previously had that same address. It's also worth contacting whoever assigned you the IP (your hosting provider or ISP) about the issue.

This tool supports IPv4 addresses, which are what most major DNSBLs cover. IPv6 is only supported by a handful of blacklists, so it isn't handled here — please enter an IPv4 address or a domain name instead.

A clean result across the major blacklists is a good sign, but mail deliverability also depends on things like your SPF/DKIM/DMARC configuration. Consider also using this site's mail deliverability checker.
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Side Note — blacklists piggyback on the DNS system itself

DNSBL (DNS-based Blackhole List) is a technique devised by the anti-spam community in the late 1990s. Its defining feature is that instead of building a dedicated database server or API from scratch, it simply repurposed the DNS query infrastructure that was already deployed worldwide. The trick is deceptively simple: reverse the octets of an IP address and build a special hostname like "2.0.0.127.zen.spamhaus.org," then send that as an ordinary A record query. If the address is listed, you get back a response code like "127.0.0.2"; if not, you get NXDOMAIN.

This approach spread widely because every mail server of the era already had DNS lookup capability built in, so no additional software or protocol was ever required to adopt it. Today's major blacklist operators — Spamhaus, SORBS, Barracuda, and others — all still rely on this same simple DNS query format.

DNSBLs are not free of false positives, though. Dynamic IP ranges, or addresses that carry a history of spam sent by a previous occupant, can remain listed regardless of who's using the address now. That's exactly why most blacklist operators provide a delisting request process — flagging a listing and requesting removal promptly is one of the most effective ways to improve deliverability.

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