Why Is My Domain on a Blacklist? (And How to Check)

A DNSBL (DNS-based blacklist) - Spamhaus, SpamCop, SORBS and others are the best known - is a list of domains and IP addresses that mail providers have flagged as sources of spam or abuse. Once a mail server or major inbox provider is checking a blacklist you are on, mail from your domain can be silently dropped, quarantined, or bounced entirely, often with no notification to you.

Common reasons a domain ends up listed

Sending to a list with a lot of stale or fake addresses (which generates spam-trap hits), a compromised account or server being used to send spam without the owner's knowledge, sudden spikes in sending volume that look automated, or - on shared hosting - a completely unrelated site on the same IP getting flagged and dragging your domain's reputation down with it.

How to check

A blacklist checker queries your domain or IP against the major public DNSBLs at once, rather than checking each one by hand, and shows exactly which lists (if any) currently have you flagged.

Catching it early

Blacklisting can happen at any time, not just after a one-off mistake - ongoing monitoring re-checks automatically and sends an alert the moment your domain is newly listed, instead of you finding out from a sudden drop in delivered mail.