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by jeffbee
1036 days ago
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I'd be surprised if this was accurate. A low-volume IP might get a temporary failure code 4xx, but that's not silent. If they accept your message they intend to deliver it, or bounce it. Perhaps your return path is defective. |
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It most often involved security log snippets which would include ip addresses and hostnames that were likely already on "is a known bad actor" list.
Bug on their end? Intentional thing to disrupt spammers? I don't know.