Microsoft 365 Outage Lasts Over 24 Hours After Network Upgrade Fault

What happened

The outage began around 1 p.m. Eastern Time on Nov 12, with Exchange Online mailbox access failing first in the Americas, then spreading to Outlook, Teams, SharePoint Online, Microsoft 365 Copilot, Defender XDR and other services. Microsoft tracked the incident in the admin center under two incident IDs, EX1550543 and MO1550821.

Downdetector data shows Outlook problem reports peaked near 130,000 around 1 p.m. on Nov 12, with Microsoft 365 reports above 47,000; at the peak, about 20,000 reports a minute came in across five Microsoft services, covering 74 countries and territories. Staff in the US House of Representatives were among those affected.

Recovery did not go smoothly: Microsoft said servers returned to service could become unresponsive again once they received traffic, and repair work stalled at one point. By 3 p.m. on Nov 13, the service health page showed all services “operational,” with most services back, though some users could still see 365 feature issues and mail flow needed more time to fully normalize.

What caused it

Microsoft said in a statement on the afternoon of Nov 13 that this was a technical issue not related to cyber or AI/agents, introduced by an issue during an earlier network capacity upgrade that surfaced following a recent network change. The company said it has no evidence of malicious activity and will publish a full post-incident report once its review is complete.

Microsoft 365 has about 430 million users worldwide. Executive Charles Lamanna wrote on X late on Nov 12, apologizing for the disruption the outage caused customers and confirming there was no indication it resulted from malicious or cyber activity.

Key facts

1. Start: Around 1 p.m. Eastern Time on Nov 12, Exchange Online mailbox access failed first in the Americas
2. Scope: Outlook, Teams, SharePoint, Copilot, Defender XDR and more went down; admin center incidents EX1550543 and MO1550821
3. Scale: Outlook problem reports peaked near 130,000, Microsoft 365 reports above 47,000, across 74 countries and territories; Microsoft 365 has about 430 million users worldwide
4. Recovery: Restored servers became unresponsive again under traffic; most services were back by 3 p.m. on Nov 13, with the health page showing “operational”
5. Cause: A technical issue not related to cyberattacks or AI/agents, introduced during an earlier network capacity upgrade and surfacing after a recent network change
6. Report: Microsoft says it will publish a full post-incident report once its review is complete