Some users may have been unable to access their Exchange Online mailboxes using the Outlook desktop client

Title: Some users may have been unable to access their Exchange Online mailboxes using the Outlook desktop client User impact: Users may have been unable to access their Exchange Online mailboxes using the Outlook desktop client. More info: Impacted users may have received a 401 error message. Final status: We’ve confirmed that reverting the change successfully remediated the impact and restored the service. Scope of impact: Some users attempting to access their Exchange Online mailboxes via the Outlook desktop client may have been impacted. Start time: Tuesday, March 24, 2026, at 5:40 AM UTC End time: Tuesday, March 24, 2026, at 1:00 PM UTC Root cause: A recent service change introduced an unexpected behaviour that prevented part of the service from operating as designed, resulting in impact. Next steps: - We'll continue to closely monitor the service to ensure it remains healthy. - We're reviewing our deployment procedures to better identify similar issues during our development and testing cycles. This is the final update for the event.

Title: Some users may be unable to access their Exchange Online mailboxes using the Outlook desktop client User impact: Users may be unable to access their Exchange Online mailboxes using the Outlook desktop client. More info: Impacted users may receive a 401 error message. Current status: We’ve identified that a recent service change may be causing impact to occur. We’ve reverted the change to restore normal service and are monitoring service data to confirm the mitigation is working as expected. Scope of impact: Some users attempting to access their Exchange Online mailboxes via the Outlook desktop client may be impacted. This information may be updated as our investigation continues. Next update by: Tuesday, March 24, 2026, at 3:00 PM UTC