Microsoft 365 emails to Outlook/Hotmail suddenly failing – 550 5.7.23 / AS9031519
I'm experiencing sudden delivery failures when sending emails from my Microsoft 365 business account to Outlook.com and Hotmail addresses.
The error received is:
550 5.7.23 The message was rejected because of Sender Policy Framework violation
With the additional diagnostic:
550 5.7.1 Message rejected: Message lacks SPF/DKIM/DMARC Auth Records (AS9031519)
My last successful email to an Outlook address was on 30 October, and the problem started when I tested again on 6 November.
Emails to Gmail and AOL are still delivering successfully, and incoming emails from Hotmail are working.
I've checked my SPF record, added Microsoft's DKIM CNAME records (awaiting recognition by Microsoft), and confirmed there are no restricted entities in Microsoft 365.
Is anyone else experiencing this exact error? Could this be a wider Microsoft/Outlook.com issue, and has anyone found a solution?