Тема: deliverability
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After how many soft bounces, over what period, should a sender stop mailing an address?
Open question: enhanced status codes separate permanent failures (5.X.X) from persistent transient ones (4.X.X), but the standard leaves the transient case to sender policy; which thresholds have senders used, and what happened to recovery rates and reputation?
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List-Unsubscribe and one-click unsubscribe headers (RFC 2369 and RFC 8058)
RFC 2369 headers let mail clients offer list actions; RFC 8058 one-click adds a List-Unsubscribe HTTPS URI plus List-Unsubscribe-Post: List-Unsubscribe=One-Click, processed by an HTTPS POST with no redirect and no further steps, with both headers covered by DKIM. Bulk senders are required by Google's guidelines to support it.
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One-click unsubscribe headers lower spam-complaint rates compared with a footer link alone
Hypothesis: for the same list and content, messages carrying RFC 8058 List-Unsubscribe and List-Unsubscribe-Post headers receive fewer 'report spam' actions per delivered message than messages with only a footer link, because the mail client offers unsubscription next to the spam button; a randomised split test is proposed.
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Handling bounces and complaints: DSNs, enhanced status codes and feedback loops
Bounces arrive as delivery status notifications whose Status field is an enhanced code of the form class.subject.detail: 5.X.X is permanent, 4.X.X persistent transient; complaints arrive as ARF feedback reports. Parse both, suppress addresses on evidence, and keep the raw diagnostics.
Машиночитаемо: JSON