Admins are unable to access the Exchange admin center (EAC)

A post-incident report has been published.

A post-incident report has been published.

A post-incident report has been published.

Title: Admins are unable to access the Exchange admin center (EAC) User impact: Admins are unable to access the EAC. More info: When attempting to access the Exchange admin center, affected admins encountered an “Internal Server Error” message. Final status: We've completed the rollback of the identified Exchange admin center (EAC) change. Service telemetry shows that errors have returned to expected levels, and user reports have confirmed that EAC access has been restored. Admins who continue to experience impact should close their existing EAC browser session, open a new session, and retry accessing the EAC. We’ll continue to monitor service health to ensure sustained service stability. Scope of impact: Impact was specific to admins attempting to access the EAC. Start time: Monday, October 12, 2026, at 8:15 AM UTC End time: Monday, October 12, 2026, at 12:50 PM UTC Root cause: During a routine service deployment, an update to the Exchange Admin Center authentication components introduced an incompatibility in the way delegated administrator access tokens were validated. When administrators accessed the Exchange Admin Center through the Microsoft 365 admin experience, the updated authentication components did not successfully validate the delegated token used for the request. The service then attempted an interactive sign-in as a fallback. That fallback could not complete because the sign-in context was associated with a different service domain, resulting in an authentication failure and an Internal Server Error. Next steps: - For a more comprehensive list of next steps and actions, please refer to the Post Incident Report document. We’ll provide a preliminary Post-Incident Report within two business days and a final Post-Incident Report within five business days.

We’ve completed the rollback and are continuing to monitor service health, with telemetry showing errors trending downward from their earlier peak. Admins who continue to experience impact should close their existing Exchange admin center (EAC) browser session, open a new session, and retry accessing the EAC. We’ll continue monitoring to validate recovery. This quick update is designed to give the latest information on this issue. Next update by: Monday, October 12, 2026, at 1:30 PM UTC

We’re continuing to roll back the identified Exchange admin center (EAC) change. Initial telemetry shows errors trending downward from their earlier peak, and we’re monitoring service health to determine whether the rollback restores access for affected admins. This quick update is designed to give the latest information on this issue. Next update by: Monday, October 12, 2026, at 1:30 PM UTC

Title: Admins are unable to access the Exchange admin center (EAC) User impact: Admins are unable to access the EAC. More info: When attempting to access the Exchange admin center, admins encounter an “Internal Server Error” message. Current status: Our testing has identified a recent Exchange admin center (EAC) configuration change as a potential contributor to the access failures and associated HTTP 302 redirects. We’re rolling back the change, which we expect to complete within approximately two hours. Once complete, we’ll monitor the environment to determine whether this resolves the impact. Scope of impact: Impact may be specific to any admin attempting to access the EAC. This information may be updated as our investigation continues. Next update by: Monday, October 12, 2026, at 1:30 PM UTC

We’re continuing to test the rollback of the recent Exchange admin center (EAC) change while monitoring the results to determine if this resolves the impact. In parallel, we’re continuing our analysis of the unexpected HTTP 302 redirects to help determine the source of the issue. This quick update is designed to give the latest information on this issue. Next update by: Monday, October 12, 2026, at 12:30 AM UTC

Title: Admins are unable to access the Exchange admin center (EAC) User impact: Admins are unable to access the EAC. More info: When attempting to access the Exchange admin center, admins encounter an “Internal Server Error” message. Current status: We’re continuing to investigate the unexpected HTTP 302 redirects and are testing a rollback of a recent Exchange admin center (EAC) change to determine if this resolves the impact. We’re also comparing results across affected environments to determine our next steps. Scope of impact: Impact may be specific to any admin attempting to access the EAC. This information may be updated as our investigation continues. Next update by: Monday, October 12, 2026, at 12:30 PM UTC

We’ve identified unexpected 302 redirect errors during affected Exchange admin center (EAC) access attempts and are analyzing diagnostic logs to isolate the source of the access failures. While we continue our investigation, admins remain unable to access the EAC, with no workaround currently available. This quick update is designed to give the latest information on this issue. Next update by: Monday, October 12, 2026, at 11:30 AM UTC

Title: Admins are unable to access the Exchange admin center (EAC) User impact: Admins are unable to access the EAC. More info: When attempting to access the Exchange admin center, affected admins may encounter an “Internal Server Error” message. Current status: We’re reviewing service logs and analyzing available diagnostic data to identify the source of the issue and determine next steps. Scope of impact: Impact may be specific to any admin attempting to access the EAC. This information may be updated as our investigation continues. Next update by: Monday, October 12, 2026, at 11:30 AM UTC

Title: Some admins may be unable to access the Exchange admin center (EAC) User impact: Admins may be unable to access the EAC. More info: When attempting to access the Exchange admin center, affected admins may encounter an “Internal Server Error” message. Current status: When attempting to access the Exchange admin center, affected admins may encounter an “Internal Server Error” message. Scope of impact: Impact may be specific to any admin attempting to access the EAC. This information may be updated as our investigation continues. Next update by: Monday, October 12, 2026, at 11:30 AM UTC