There's a lot of variation in what 4xx and 5xx mean in practice. This means there's room for some senders to spend time investigating and understanding what each receiving domain's 4xx and 5xx (and subcategories thereof) actually mean for address delivery over time, and for designing rules and policies to handle them based on observed outcomes - IF those are a more reliable indicator than the general guidance from RFCs.
That doesn't mean Luke is ignoring null MXes. On Sat, Feb 25, 2023 at 8:00 PM Benny Pedersen via mailop <mailop@mailop.org> wrote: > Luke via mailop skrev den 2023-02-26 04:15: > > I can assure you sendgrid retries 4xx. We also don't retry 4xx. We > > also retry 5xx. We also don't retry 5xx. How is it 2023 and people > > still think 4xx means retry and 5xx means don't retry? > > what books do you read ? > > maybe rfc 7505 is soon or later for all ? > _______________________________________________ > mailop mailing list > mailop@mailop.org > https://list.mailop.org/listinfo/mailop >
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