Blocklists are shared databases. A receiving server asks one of them a quick question, is this IP or domain listed, and acts on the answer. A listing on a respected list can block your mail across many providers at once.
Types
- IP lists name sending addresses. Most of the well-known ones work this way.
- Domain lists name domains seen in spam, whatever IP they came from. These matter more as IP addresses become easier to rotate.
- URL lists name domains that appear in message links.
Lists differ widely in how strict they are and how they list. Some act on a single spam trap hit, others look at patterns over time.
How you end up on one
- You send to spam traps.
- A burst of complaints, or a complaint rate that is too high.
- A compromised account or leaked credentials sending spam in your name.
- Mail to a purchased or scraped list.
- On a shared IP, someone else’s behaviour.
Checking and removing
- Look up your sending IP addresses and domain with a blocklist lookup tool.
- Read the listing page, which usually states the reason.
- Fix the cause before you ask for removal.
- Submit the removal request through the list’s own process.
Blocklists and Amazon SES
On shared IPs the addresses belong to AWS and are shared with other senders. On a dedicated IP the listing is yours to resolve. In both cases, a sudden leaked-credential blast is the fastest way to end up listed, so a sudden jump in send volume is worth an alert of its own. See sender reputation for the bigger picture.
Common questions
Am I on a blocklist if my mail goes to spam?
Not necessarily. Spam placement has many causes, and blocklists are only one. Check your authentication and rates first, then run a blocklist lookup.
Can I pay to be removed?
Be careful with any list that charges for removal. The reputable ones remove listings for free once the cause is fixed. Fix the cause first, or the listing returns.