Just a very, very short post with links to the Yahoo and Google requirements FAQs. Given I can’t ever remember them I’m guessing lots of y’all can’t either.
Yahoo: https://senders.yahooinc.com/best-practices/ and https://senders.yahooinc.com/faqs/
Google: https://support.google.com/a/answer/14229414
Seen this recently?
451 Message temporarily deferred due to unresolvable RFC.5321 from domain; see https://postmaster.yahooinc.com/error-codes
Every once in a while we’ll see a rejection from Yahoo that says RFCs 554 5.0.0 Message not accepted due to failed RFC compliance. What does that mean and what can we do about it?
If you’re an ESP with small customers you may have looked at the recent Google / Yahoo requirements around DMARC-style alignment for authentication and panicked a bit.
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