What Is a DNSBL?
A DNSBL (DNS-based Blackhole List) is a public, real-time list of IP addresses associated with sending spam. Mail servers around the world check these lists before accepting incoming email — if your sending IP shows up on one, your messages may be silently rejected or routed straight to the recipient's spam folder, even if the content is completely legitimate.
What to Do If You're Listed
- Find the cause first. Common reasons: a compromised server sending spam without your knowledge, a misconfigured mail relay, or a shared IP that a different tenant abused.
- Fix the underlying issue before requesting removal — most blacklists will simply re-list you if the problem isn't actually resolved.
- Submit a delisting request through the specific blacklist's own website — each one has its own process and timeline, typically a day or two.
- Set up SPF, DKIM and DMARC if you haven't already (see our SPF/DKIM/DMARC Checker) — proper authentication makes it much harder for spammers to abuse your domain in the first place.