What is a trap domain?
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A trap domain is a whole domain that catches senders, not just one address. Two kinds show up. Expired domains often get re-registered by squatters, which is when dead domains become trap domains, a separate and worse problem than the domain simply being dead. And typo trap domains are common misspellings of the big mailbox providers (gmal.com, gnail.com, yahooo.com, hotmai.com), registered with mail servers running so every sender that delivers there gets logged.
No real subscriber can receive mail at those domains, so a hit says you accepted an invalid address at signup and kept mailing it. If you have addresses on them, suppress them. If you're hitting trap domains on current campaigns, that's worth escalating.
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