Help & Troubleshooting
Blacklists (DNSBL)
What this is
DNS-based blacklists (DNSBLs) enumerate IP addresses observed sending spam. Most mail providers consult several of them; being listed on a widely-used one measurably hurts delivery.
How to read your result
Clean on all zones is the goal. A single listing on an obscure list matters little; a listing on a major zone (e.g. Spamhaus) demands action. Listings apply to the IP, not the domain — shared IPs share their reputation.
Common problems and how to fix them
Listed on a major blacklist
How it shows up: Widespread bounces referencing the blacklist by name, or sudden delivery collapse to major providers.
How to fix it: First stop the cause — a compromised account, an infected machine, an open relay, or genuinely spammy sending. Then request delisting via the specific list's process (each has its own form). Delisting without fixing the cause leads to prompt relisting.
Inherited a dirty IP
How it shows up: A brand-new server is listed before you sent a single message — the previous tenant burned the address.
How to fix it: Request delisting citing new ownership, or ask the provider for a different IP. Check candidate IPs before pointing production mail at them.
Listed on tiny or pay-to-delist zones only
How it shows up: A scanner shows "listed" on lists you have never seen referenced in real bounces.
How to fix it: Verify whether real receivers actually use that list (bounce messages tell you). Ignore extortionate pay-to-delist operations; reputable lists never charge for delisting.