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Outlook.com bounces legit emails as Microsoft's authentication crackdown goes sideways

The company's consumer email services are affected, and it appears that if a domain doesn't have working SPF or if it has a missing DMARC record, then Outlook.com and its ilk will treat it as suspicious and not accept emails.

✦ Extractive summary — built from the sources' own reporting•From 1 source•1 min read•Updated November 9, 2026, 1:30 PM UTC
Key points
  • A moderator in Microsoft's support forum acknowledged the bug and said it was "classified as a service degradation." "Microsoft is actively investigating the underlying cause of this email delivery issue, and engineering teams are actively analyzing service telemetry and customer-provided data to identify the source of the issue." Still.
  • Although some customers insist their DMARC, SPF, and DKIM settings are compliant, many more have reported that once they set them to Microsoft's preferences, email began flowing once more.
  • The troubles began at the end of last week and appear to be the result of Microsoft tightening the rules (or at least attempting to do so) for accepting emails.

A validation error has stopped Outlook.com from accepting legitimate emails.

In 2025, Microsoft announced new rules designed to strengthen email authentication for domains sending more than 5,000 emails per day.

Additional details
  • Other users have reported errors highlighting a lack of DMARC (Domain-based Message Authentication, Reporting, and Conformance) information.
  • Earlier today, several users in Europe, the Middle East, and Africa were affected by another Microsoft whoopsie – a "recent service change" that caused some connections to be abruptly terminated.
  • The problem appears widespread and, according to reports from affected users, can result in non-delivery reports with error codes related to SPF (Sender Policy Framework) validation failures.
  • According to complainants in the Outlook forum, a single email with just one line might now be rejected.
  • Outlook on the web, as well as the Purview and Defender portals were all affected.

How this summary was made: extractive summary — built from the sources' own reporting. It is drawn only from the reporting of the sources listed below — read the originals for full detail. How we summarize →

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The RegisterNovember 9, 2026, 1:30 PM UTC →

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