Question 1

What is a blacklist (DNSBL)?

Accepted Answer

A DNS blocklist (DNSBL, sometimes RBL) is a published list of IP addresses — and sometimes domains — that a provider has flagged for sending spam or abuse. Mailbox providers query these lists in real time when they receive your mail; a listing on a major one can send your messages to spam or get them rejected at the door. This tool queries a dozen well-known lists at once for the IP or domain you enter.

Question 2

What does it mean if my IP is listed?

Accepted Answer

It means at least one blocklist has flagged that IP, and receivers who trust that list may throttle, spam-folder, or reject mail from it. The impact depends on the list — a Spamhaus listing is far more consequential than a small niche one. Any listing is worth investigating: find the cause (a compromised account, a dirty list, a shared IP neighbor), fix it, then request removal at the specific provider.

Question 3

How do I get removed from a blacklist?

Accepted Answer

Each list runs its own removal (delisting) process on its website — you look up the IP there and follow its steps. But delisting only sticks if you fix the underlying cause first: stop the spam source, clean your list, and confirm your authentication. Many lists re-list automatically if the bad behavior continues, and some expire listings on their own once the abuse stops.

Question 4

Why does a list show “No answer”?

Accepted Answer

Some blocklists — Spamhaus and Barracuda in particular — restrict free queries from shared or cloud resolvers and answer with a special code instead of a real result. When that happens we mark the list “No answer” rather than guess, so a blocked query is never mistaken for a clean or a listed result. Query those lists directly from your own resolver, or use continuous monitoring, for an authoritative answer.

Question 5

Should I check my IP or my domain?

Accepted Answer

Check the IP your mail actually sends from — that's what receivers evaluate against IP blocklists. If you enter a domain, this tool resolves its A record and checks that IP, which is a reasonable proxy but may not be your true sending IP if you send through an ESP. For an ESP, your mail usually goes out on the provider's shared or dedicated IPs, which they manage.

Blacklist checker.

Listed? Do this next

Why listings happen — and how to avoid them

Blacklist checker — FAQ