Email blocklists: how to check them and how to get off one

What a blocklist actually is

A blocklist (the older word is blacklist) is a published set of IPs or domains that some observer has associated with spam. Receiving servers choose which lists to consult. That word "choose" is the key to the whole topic: a listing only matters to the extent that servers you care about actually use the list.

A handful of lists — Spamhaus above all — are consulted so widely that a listing is an emergency. Hundreds of others are consulted by almost nobody, and a listing there is trivia.

How to find out you are listed

• The bounce tells you. Rejections caused by a blocklist usually name it in the SMTP response, often with a lookup URL. Read your bounces before reaching for a checker tool.
• Multi-list checkers. Free tools query dozens of DNSBLs for your IP and domain at once. Useful as a periodic habit — with the caveat that most of the lists they check do not matter.
• The symptom pattern. A blocklist problem is usually sudden and provider-shaped: delivery to one provider collapses overnight while others are unaffected.

Getting delisted

Fix the cause before requesting removal. Every serious list re-lists quickly if the behaviour continues, and repeat listings are harder to shed. The cause is usually one of: a compromised account or form, a purchased list, a burst of mail to decayed addresses, or an open relay.

Then use the list's own process. Spamhaus and most major lists have self-service lookup and removal, free. Some smaller lists simply expire entries after a clean period, and the correct action is to wait.

Nobody legitimate charges for delisting. A list that demands payment for removal is running an extortion business, and — conveniently — the lists that do this are the ones no real mail server consults. Paying tells them you will pay again.

Keeping it from recurring

The listing was a symptom. The durable fixes are the boring ones: validate addresses at collection, suppress bounces automatically, watch complaint rates per provider, and secure every form and SMTP credential that can originate mail. A spam-trap hit — the classic Spamhaus trigger — is almost always a stale list segment that hygiene would have retired.

Common questions

Keep reading

• The email deliverability checklist
• How to reduce spam complaints
• How to reduce email bounce rate