Microsoft's Rejection Phase Is Live: A 550 5.7.515 Field Guide
Outlook now hard-rejects non-compliant bulk mail with 550 5.7.515, and Safe Senders cannot override it. Diagnosing the bounce and fixing the authentication behind it.
#Outlook
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Microsoft's New Outlook Sender Requirements: A Compliance Guide
Microsoft now requires SPF, DKIM, and DMARC from high-volume senders to Outlook consumer domains. What the rules demand, how enforcement works, and how to comply.