Listed on a blocklist: what to do, in order

Delivery to several providers stops at once. Responses mention a URL. You are on a blocklist.

The instinct is to request delisting immediately. That is the last step, not the first, and doing it first usually means being relisted within days — often with a longer minimum listing period.

Step 1: which list

The SMTP response usually names it. If not, check the sending IP and your sending domain against the major lists — they are separate, and being clean on one says nothing about the other.

Not all listings matter equally. A listing on a major list that large providers consult will stop delivery outright. A listing on an obscure one that nobody queries may have no effect at all. Check your actual delivery data before treating a listing as the cause of a problem it may not be causing.

Step 2: why

Most lists publish a reason, and it is usually one of:

Spam traps. You sent to an address that exists only to catch senders. Either a recycled address — one that was real, went dormant, and was repurposed — or a pristine one that was never valid and got onto your list through scraping or a purchase.

Complaint volume. Enough recipients marked your mail as spam.

Compromise. Something on your network is sending mail you did not authorise. Check the queue and the authentication logs before anything else, because this is the one failure mode that gets worse while you investigate.

Configuration. Missing reverse DNS, a HELO name that does not match, an open relay. The easiest to fix and the easiest to prevent.

Step 3: fix it

Actually fix it. Delisting a sender whose cause is unresolved produces a second listing with a longer minimum period, and some lists stop accepting requests from a sender who has been through the cycle repeatedly.

• Traps — audit how addresses enter your list. Remove anything unengaged for a long period. If you ever bought or scraped a list, that is the cause.
• Complaints — see reducing complaint rate. Shorter term: reduce frequency and send only to recent engagement.
• Compromise — find it, close it, rotate credentials, and check what was sent so you know the scale of what recipients received.
• Configuration — fix the PTR, the HELO, the relay, and verify with a test message before requesting anything.

Step 4: request removal

Most lists have a self-service form. Some auto-expire listings after a quiet period. A few require an explanation, and those read what you write.

Say what the cause was and what you changed. "Please remove" with no detail is ignored. A specific account of what happened and what is different now is usually accepted.

Afterwards

Resume at reduced volume, not at full. An IP that was listed, got delisted and immediately returns to full volume gets relisted. Treat it as a partial warmup.

Then monitor, because the listing was a symptom. The underlying reputation problem takes longer to recover than the listing does to clear.