Outlook.com Rejects Legitimate Emails Over Authentication
Microsoft is investigating a service degradation that has caused some valid messages to bounce due to SPF and DMARC validation failures.
Updated on Nov. 9, 2026 in Cybersecurity
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Outlook.com has been rejecting legitimate emails, producing non-delivery reports with SPF validation error codes and, for some users, errors citing missing DMARC information. The problems began at the end of the prior week, and Microsoft has acknowledged the delivery issue as a service degradation it is investigating.
Why it matters
Outlook.com treats domains without working SPF or a missing DMARC record as suspicious, so senders can lose legitimate mail when validation fails. Microsoft tightened authentication rules in 2025 to curb spam and bulk abuse, and the rejections highlight how stricter filtering can affect valid senders.
Microsoft's 2025 requirements apply to domains sending more than 5,000 emails per day, mandating DMARC, SPF, and DKIM compliance. Microsoft has not yet identified what caused the validation failures, and the error messages do not clearly explain why individual bounces occurred.
The players
Microsoft
Microsoft is the technology company that operates Outlook.com and enacted the 2025 email authentication requirements for bulk senders.
Outlook.com
Outlook.com is Microsoft's free email service, which applies SPF and DMARC checks to incoming mail.
The details
Affected emails were returned with SPF validation failure codes, and some users saw messages indicating no DMARC information was present. Many users reported that delivery resumed after they configured DMARC, SPF, and DKIM to Microsoft's preferences, and a resend attempt may sometimes succeed.
Timeline
2025: Microsoft announced DMARC, SPF, and DKIM requirements for bulk senders.
End of last week: Outlook.com validation problems began.
November 9, 2026: A separate Microsoft service change disrupted Outlook connections in Europe, the Middle East, and Africa earlier that day.
Tech Race
Microsoft's 2025 DMARC, SPF, and DKIM requirements for bulk senders set the enforcement baseline that the current Outlook.com rejections now test. The episode shows how the same authentication rules meant to block spam can also block valid mail when validation breaks.
Users who send mail from their own domains may need to verify their SPF, DKIM, and DMARC records, since messages that fail validation can be silently rejected. Resending a bounced message may succeed because the glitch is intermittent.
The takeaway
Checking that your domain's SPF, DKIM, and DMARC records are accurate can help prevent legitimate email from being rejected during periods of strict filtering. Retrying a failed send may also be worthwhile while the intermittent problem persists.
Further reading
Explore more in Cybersecurity coverage on email authentication and security threats.
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