Users may be unable to access Outlook on the web from a specific Outlook link

Title: Users may be unable to access Outlook on the web from a specific Outlook link User impact: Users may have been unable to access Outlook on the web from a specific Outlook link. More info: Users may have been unable to access Outlook on the web from a specific link within Outlook. Users may have been access Outlook on the web by navigating to a direct URL with /mail/ appended. As an example, some users could navigate to "https://outlook.office365.com/mail/" to successfully access the client. Final status: We've reverted the problematic code change, and confirmed through monitoring service health telemetry that the impact has been remediated. Scope of impact: This issue may have prevented any user attempting to access Outlook on the web from the specific link in the More Info portion of this communication. Start time: Tuesday, September 15, 2026, at 3:00 PM UTC End time: Friday, September 18, 2026, at 3:40 PM UTC Root cause: A recent code change was producing a code regression that was preventing users from accessing Outlook on the web from a specific link within Outlook. Next steps: - We're reviewing our update procedures to understand why impact to Outlook on the web access wasn't caught during the testing phase. This will allow us to drive service improvements by proactively identifying similar issues in the future and improve our update testing processes. This is the final update for the event.

Title: Users are unable to access Outlook on the web from a specific Outlook link User impact: Users are unable to access Outlook on the web from a specific Outlook link. More info: Users are unable to access Outlook on the web from a specific link within Outlook. Users can access Outlook on the web by navigating to a direct URL with /mail/ appended. As an example, some users can navigate to "https://outlook.office365.com/mail/" to successfully access the client. Department of Defense customers: https://webmail.apps.mil/mail/ GCCH customers: https://outlook.office365.us/mail/ Current status: Our change reversion is approximately 82 percent complete, and our established timeline expects it will have completed by our next scheduled communication update.‌ Scope of impact: This issue may prevent any user attempting to access Outlook on the web from the specific link in the More Info portion of this communication. This information may be updated as our investigation continues. Start time: Tuesday, September 15, 2026, at 3:00 PM UTC Root cause: A recent code change is producing a code regression that is preventing users from accessing Outlook on the web from a specific link within Outlook. Next update by: Friday, September 18, 2026, at 9:00 PM UTC

Title: Users are unable to access Outlook on the web from a specific Outlook link User impact: Users are unable to access Outlook on the web from a specific Outlook link. More info: Users are unable to access Outlook on the web from a specific link within Outlook. Users can access Outlook on the web by navigating to a direct URL with /mail/ appended. As an example, some users can navigate to "https://outlook.office365.com/mail/" to successfully access the client. Department of Defense customers: https://webmail.apps.mil/mail/ GCCH customers: https://outlook.office365.us/mail/ Current status: We've determined that a recent code change is preventing users from accessing Outlook on the web from a specific link within Outlook. We've conducted our change reversion process to address the code issue and to remediate the impact. We're monitoring the environment to ensure no other impact persists and that the issue is resolved. Scope of impact: This issue may prevent any user attempting to access Outlook on the web from the specific link in the More Info portion of this communication. This information may be updated as our investigation continues. Start time: Tuesday, September 15, 2026, at 3:00 PM UTC Root cause: A recent code change is producing a code regression that is preventing users from accessing Outlook on the web from a specific link within Outlook. Next update by: Thursday, September 17, 2026, at 9:00 PM UTC

Title: Users may be unable to access Outlook on the web from a specific Outlook link User impact: Users may be unable to access Outlook on the web from a specific Outlook link. Current status: We're investigating a potential issue with the Exchange Online service and are checking for impact to your organization. We'll provide an update within 30 minutes.