The Microsoft 365 outage entered its second day on Tuesday, with the company still unable to declare a full resolution after a misconfiguration in core authentication infrastructure knocked out email, file access, and collaboration tools for business and enterprise customers across the globe.
The fault originated in Microsoft’s Exchange Online service. According to BleepingComputer, Microsoft tracked the incident under identifier MO1465074 and attributed it to ‘core authentication configuration issues used by multiple internal services within the Exchange Online infrastructure.’
What the Microsoft 365 Outage Actually Broke
The disruption spread well beyond Outlook. Microsoft‘s own status page listed SharePoint Online, OneDrive for Business, Teams, Copilot, Purview, Defender XDR, the Microsoft 365 Admin Centre, and Universal Print as affected services.
The user-facing consequences were sharper than a typical mail-delay event. BleepingComputer reported that some customers were unable to download email attachments through any Exchange Online connection method, and others found they could not sign in to Outlook on the web at all.
The underlying problem, Microsoft said, was preventing authentication components from ‘deploying as expected to a portion of infrastructure.’ That phrasing points to a configuration change that broke the mechanism services use to verify user identity, cascading across the entire Microsoft 365 stack.
The Overnight Recovery Effort
Microsoft moved methodically through the night. At 7:47 p.m. ET on Monday, the company’s official Microsoft 365 status account on X said it was ‘restarting targeted sections of the affected infrastructure to aid the recovery of the downstream scenarios’ alongside its mitigation deployment, according to Mashable.
By 10 p.m. ET, mail flow was improving but search remained degraded. Shortly after 3 a.m. ET on Tuesday, Microsoft posted that search functionality was also recovering. The company’s language remained carefully qualified: ‘indications from telemetry remain positive’ and ‘mitigation actions are continuing to progress’ are assurances of direction, not arrival.
Microsoft said it had entered a period of extended monitoring to confirm a complete fix before declaring the incident closed.
What Comes Next: The Post-Incident Review
For customers wanting a fuller explanation, a formal post-incident review is likely on its way. According to Microsoft’s Tech Community blog on incident transparency, the company publishes post-incident reviews within three days for major events and within 14 days for smaller multi-service incidents.
Those reviews take the form of narrative, timeline-driven analyses that map cascading dependencies and mitigation actions, rather than settling on a single root cause. Given that this Microsoft 365 outage touched authentication infrastructure shared by at least eight distinct services, the dependency chain is unlikely to be short.
The practical question for IT teams right now is whether the ‘extended monitoring’ phase produces a clean all-clear before the business day peaks on Tuesday or stretches into a third day. Microsoft’s next update on X is the one to watch.
