Also called: blacklist
A blocklist is a list of IP addresses or domains that mailbox providers and spam filters have flagged as unsafe or unwanted; a sender's mail lands in spam or gets rejected outright at any receiver that checks its domain or IP against one.
A blocklist, also called a blacklist, is a list an operator maintains of IP addresses or domains it considers untrustworthy: known spam sources, compromised servers, senders with a pattern of complaints or spam-trap hits. Mailbox providers and mail servers check incoming mail against one or more of these lists before deciding whether to accept it. There's no single central blocklist. Dozens of operators run their own, each with its own criteria and its own delisting process.
Stop sending from that domain right away, not just from whichever campaign triggered the flag. Continuing to send while a listing is active makes the problem worse instead of pausing it. Then find out which specific blocklist flagged the domain, since each one runs its own delisting process, and fix whatever actually caused it, whether that's list quality, a volume spike, or a content pattern, before requesting removal.
Delisting takes days, not hours, on most blocklists, and a domain should stay paused for sending the whole time it's under review. Getting listed once doesn't mean a domain is permanently damaged. It means something in the sending pattern tripped a specific operator's rule, and that operator needs to see the pattern stop before it takes the domain off the list.
Keep the sending domain separate from the company's main domain specifically so a blocklist hit never touches the mail that actually has to land: invoices, password resets, support replies. Rotating in a fresh sending domain is sometimes faster than waiting out a stubborn delisting process, especially for a domain that was disposable infrastructure to begin with.
People treat a blocklist listing as a single, universal judgment, 'my domain is blacklisted,' as if there's one list and one verdict. There isn't. A domain can be clean on every major list and still flagged on one obscure one that a particular corporate mail server happens to check, and the fix is always specific to whichever list actually flagged it, not a generic reputation repair.
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