Outlook.com rejects legitimate mail over authentication checks
The Register reported on November 9, 2026, that Microsoft Outlook.com was rejecting some legitimate emails, after failures began late the previous week. The publication cited user reports of non-delivery errors involving Sender Policy Framework (SPF) validation failures or missing Domain-based Message Authentication, Reporting, and Conformance (DMARC) information.
SPF and DMARC records help receiving services check whether a message is authorized to come from its claimed domain. If those records are missing or fail validation, Outlook.com may treat genuine business or transactional mail as suspicious and refuse delivery.
For organizations sending to Outlook.com recipients, delivery can depend on the authentication records for their sending domains, even when the messages are legitimate. The report does not establish the issue’s scope or a fix.
Microsoft's email security is unexpectedly blocking legitimate business mail
Inconsistent filtering, whether from a bug or a policy change, is bouncing legitimate messages sent to Outlook, Hotmail, and other Microsoft consumer accounts, with error messages citing missing or failed email authentication.