Microsoft Exchange Online outage causes email failures, auth issues - BleepingComputer
Microsoft is investigating a widespread service issue causing authentication issues, connection problems, service delays and failures, and various other issues for Microsoft 365 customers. However, while Exchange Online is the most impacted service, Microsoft revealed in a new incident report (MO1465074) that this outage also impacts multiple other Microsoft 365 services, including OneDrive for Business and SharePoint Online, Microsoft Teams, Microsoft Purview, and Microsoft Defender XDR. Microsoft confirms outage affecting search in Microsoft 365 apps Microsoft working to fix Exchange Online mailbox quarantine issue Nearly 22,000 Microsoft Exchange servers vulnerable to hijack attacks Brave browser adds email aliases to help users evade tracking Microsoft rolls out Classic Outlook theme for New Outlook users
Microsoft is investigating a widespread service issue causing authentication issues, connection problems, service delays and failures, and various other issues for Microsoft 365 customers.
It first acknowledged the incident (tracked under EX1464935 in the admin center) at 5:30 PM UTC, when it began investigating a stream of reports from users on social media regarding multiple issues affecting Exchange Online.
However, while Exchange Online is the most impacted service, Microsoft revealed in a new incident report (MO1465074) that this outage also impacts multiple other Microsoft 365 services, including OneDrive for Business and SharePoint Online, Microsoft Teams, Microsoft Purview, and Microsoft Defender XDR.
According to outage tracking service Downdetector, tens of thousands of Outlook and Microsoft 365 users are affected and experiencing issues receiving emails via Outlook and accessing Microsoft cloud services.
Microsoft says the list of Exchange Online symptoms includes:
Although the company has yet to reveal which regions are impacted, it has classified this outage as an incident, which is typically used to describe critical service issues with noticeable user impact.
"We've isolated a common failure pattern across affected Exchange Online requests that is associated with authentication and protocol connectivity," Microsoft added in the latest admin center update.
"We're analyzing service telemetry to identify the underlying source of impact and validate potential remediation options. Additionally, we're continuing to assess the scope of impact and monitor for additional affected scenarios."
Microsoft has addressed multiple Exchange Online outages in recent months, most recently in June, when it mitigated a widespread service issue affecting the mail flow pipeline for customers across North America, Asia-Pacific (APAC), and Europe.
In April, it also resolved Exchange Online mailbox access issues that had intermittently impacted Outlook mobile and macOS users for weeks, and an Exchange Online outage that prevented users from accessing their mailboxes via Outlook on the web, Outlook desktop, Exchange ActiveSync, and other Exchange Online connection protocols.
Update August 31, 14:29 EDT: Microsoft blames the outage on core authentication configuration issues.
"We've identified issues related to a core authentication configuration used by multiple internal services within the Exchange Online infrastructure," Microsoft said. "We're performing a manual test on the individual server level to reset to configurations to validate if this resolves the issue."
Update August 31, 15:09 EDT: Microsoft now tracks this outage under MO1465074 and says the incident also affects OneDrive for Business and SharePoint Online, Microsoft Teams, Microsoft Purview, and Microsoft Defender XDR.
Update August 31, 16:12 EDT: Revised title after confirmation that the outage affects multiple Microsoft 365 services.
Update September 01, 10:29 EDT: 22 hours after the outage was first acknowledged, Microsoft says telemetry data shows "positive recovery trends."
"We're continuing to apply the targeted remediation across the remaining affected infrastructure where needed. Service telemetry continues to show positive recovery trends, with availability improving across previously impacted scenarios," Microsoft noted in an update on its Service Health Status page. "We're actively validating that authentication, connectivity, and search experiences are returning to expected service levels, while maintaining enhanced monitoring to ensure improvements are sustained and any residual impact is addressed."
Update September 01 2026 12:02:13 EDT: Microsoft says Exchange Online mail flow and search have now been restored.
"Core Exchange Online experiences, including mail flow and search functionality, have recovered. Our focus has shifted toward validating recovery across remaining Microsoft 365 services," it said. "We're actively monitoring service health, assessing any residual pockets of impact, and confirming end-to-end functionality across affected workloads."
Overall prevention scores can hide what happens after initial access. Once attackers are using valid credentials, prevention drops sharply.
The Blue Report 2026 measures defenses technique by technique across 338 million simulations run in customer production environments.
Microsoft confirms outage affecting search in Microsoft 365 apps
Microsoft working to fix Exchange Online mailbox quarantine issue
Nearly 22,000 Microsoft Exchange servers vulnerable to hijack attacks
Brave browser adds email aliases to help users evade tracking
Microsoft rolls out Classic Outlook theme for New Outlook users