Microsoft 365 Outage Caused by Maintenance Bug in Azure West US Region
Key Takeaways
- ▸Massive Microsoft 365 outage on July 23, 2026, affected West US region for 3+ hours, with 2,403 Downdetector reports within minutes
- ▸Multiple critical services impacted including OneDrive, SharePoint, Teams, Loop, and dozens of Azure services affecting enterprise cloud infrastructure
- ▸Root cause: automated maintenance system bug incorrectly removed IP routes from unintended network devices, disrupting regional connectivity
Summary
Microsoft experienced a massive outage on Thursday, July 23, 2026, affecting Microsoft 365 services starting at 10:44 AM ET. Downdetector recorded 2,403 outage reports within minutes, sharply above its normal baseline of 29. The incident primarily impacted customers in the West US Azure region, with SharePoint accounting for 78% of complaints, followed by Excel at 11% and the Microsoft 365 Admin Center at 6%.
The outage disrupted multiple critical services including OneDrive, SharePoint Online, Microsoft Teams chat functionality, the Microsoft 365 Admin Center, Power Automate, Copilot Chat, and Microsoft Loop. Beyond Microsoft 365, the incident cascaded to dozens of Azure services including Azure App Service, Azure Kubernetes Service, Azure AI Search, Azure Monitor, Azure Cosmos DB, and Azure Virtual Desktop. Microsoft Defender customers also experienced delays receiving support from Microsoft Defender Experts.
Microsoft's preliminary Post Incident Review revealed the root cause: a bug in its automated network maintenance request system. During routine device maintenance in the West US datacenter, the system incorrectly marked additional network devices as part of the maintenance event. This caused IP routes to be removed from more devices than intended, disrupting network traffic entering or leaving the West US region.
Microsoft resolved the incident by 2:26 PM ET through reverting the problematic networking change. The company has advised customers to review their business continuity and disaster recovery plans in light of the incident.
- Outage resolved by 2:26 PM ET through network change reversion; Microsoft recommends customers review business continuity plans
