CSUSM - Notice history

Microsoft in incrementally rolling out a fix for the issue. Access has largely been restored, but some users report certain browsers are still not able to log into Outlook. If you have trouble logging in, please try a different browser. We will continue to monitor the issue through resolution.

More info from Microsoft:

We've confirmed that the authentication component issue impacts other services beyond Exchange Online.

Users may experience a variety of symptoms related to this event, including but not limited to:

- Delays, failures, or incomplete results when searching for content within Exchange Online mailboxes.

- Delays or failures when sending or receiving email messages.

- Authentication-related errors when accessing Exchange Online services.

- Difficulties accessing or performing actions within Exchange administration experiences.

- Intermittent failures affecting mailbox operations and message delivery workflows.

Scope of impact

This issue may impact users attempting to send or receive email messages through Exchange Online. We're continuing our investigation to determine the full scope of affected scenarios and will provide additional information as it becomes available.

Preliminary root cause

An issue within a core authentication configuration used by multiple Microsoft 365 services is resulting in impact.

Current status

Aug 31, 2026, 1:36 PM PDT

We're reexamining recent changes made to the service to determine why the authentication components aren't being deployed as expected. Additionally, we are exploring every avenue to safely restore the components, including potentially reverting an update the affected infrastructure recently received. We're performing additional tests to evaluate the best course of action moving forward.

Microsoft has identified a potential corrective action for the affected infrastructure and are evaluating deployment options. They are monitoring service telemetry and affected Exchange Online transactions to determine whether the action is reducing impact and to better understand the scope of affected scenarios.

We implemented a fix and are currently monitoring the result.