Blacklist (DNSBL) Checker

What is a DNSBL?

A DNSBL (DNS-based blocklist, sometimes called an RBL) is a list of IP addresses or domains that have been seen sending spam or abuse. Receiving mail servers query these lists in real time over DNS as a message arrives, and a listing can result in the message being rejected outright or filed as spam.

Listings are not permanent: when the underlying problem is fixed, you request delisting at the list operator. The key is to find out you are listed before it quietly tanks your delivery.

Which lists this checker queries

For an IP we query the free public zones Spamhaus ZEN (which combines the SBL, XBL, and PBL), SpamCop, and Barracuda. For a domain we query the Spamhaus DBL (domain blocklist). These reflect each operator’s current data at query time.

A note on accuracy: some zones (such as the Spamhaus PBL) list ranges of dynamic/residential IPs that are simply not meant to send mail directly — a listing there is expected for a home connection and is not an abuse mark. The result tells you which specific zone reported a hit.

How this checker works

For an IP, we reverse the address and query each blocklist zone; a returned 127.0.0.x answer means the IP is listed in that zone. For a domain, we query the domain zone the same way. We report each zone checked and whether it returned a listing, so you know exactly where to request delisting.

Frequently asked questions

I’m listed — what do I do now?

Go to the operator of the specific zone that reported the hit (for example Spamhaus or SpamCop) and follow its delisting process. First fix the root cause — a compromised account, an open relay, a misconfigured form, or a bad list — otherwise you will be relisted. Delisting before fixing the cause is temporary.

Why is my brand-new or residential IP listed?

Some zones list dynamic and residential IP ranges (e.g. the Spamhaus PBL) on the assumption that they should send through their provider’s smarthost rather than directly. If you run a real mail server on such an IP, either send through your provider’s relay or ask for the range to be reclassified.

How often do blocklists update?

Continuously. Listings can appear within minutes of detected abuse and are removed when the operator’s criteria are met or you request delisting. Because of this you should check periodically, not just once — a clean result today does not guarantee a clean result next week.

What is the difference between an IP and a domain blocklist?

IP blocklists list the sending server’s address; domain blocklists (like the Spamhaus DBL) list domains that appear in spam — in the From address, links, or the message body. A domain can be listed even when your sending IP is clean, which is why this tool checks whichever you enter.