Users unable to access their Exchange Online mailboxes or their calendar functionality in Microsoft Teams

Issue ID: MO941162
Affected services: Exchange Online, Microsoft 365 suite, Microsoft Teams
Status: Service degradation
Issue type: Incident
Start time: Nov 25, 2024, 4:54 AM GMT+2

User impact
Users may be unable to access their Exchange Online mailboxes or their calendar functionality in Microsoft Teams.

More info
The affected scenarios are as follows:

Users may be unable to access Exchange Online using the following impacted connection methods:
- Outlook on the web
- Outlook desktop client
- Representational State Transfer (REST)
- Exchange ActiveSync (EAS)

Users may also be unable to access or modify their calendar in Microsoft Teams. This would include loading calendar, viewing meetings, creating/updating meetings and joining meetings.

Scope of impact
Some users may intermittently be affected by this issue when attempting to access their mailboxes using any connection method in Exchange Online or attempting to use their calendar in Microsoft Teams.

Preliminary root cause
A portion of infrastructure which supports mailbox and calendar functionality isn't operating as expected, resulting in impact.

Current status
Nov 25, 2024, 10:54 AM GMT+2
While we’re continuing the restarts to improve service availability, we’re thoroughly analyzing recent changes and the specific failure path to determine the next steps required to resolve the issue.
Next update by:
Monday, November 25, 2024 at 1:00 PM GMT+2

History of updates
Nov 25, 2024, 10:18 AM GMT+2
Nov 25, 2024, 9:21 AM GMT+2
Our ongoing service monitoring has determined that the issue is not limited to users in Asia Pacific, and instead that all users worldwide could be intermittently impacted. As such, we're expanding our restart efforts to ensure the issue is resolved for all users.
Nov 25, 2024, 7:46 AM GMT+2
We're continuing to work to restart the small subset of machines which have previously failed to restart. We're also continuing to add additional capacity to the affected environment to mitigate impact as quickly as possible. At this time, we expect the majority of users will experience relief from impact as we work to address the remaining issues.
Nov 25, 2024, 6:56 AM GMT+2
We've identified a small subset of machines which are failing to restart, resulting in persisting impact. We're further investigating what is causing the restarts to fail to determine our next steps.
Nov 25, 2024, 6:18 AM GMT+2
Nov 25, 2024, 5:50 AM GMT+2
We've determined via our internal telemetry that the impact to Microsoft Teams calendars has self-recovered. To fully resolve the issue, we initiated restarts on affected infrastructure and are monitoring further to determine whether additional steps are required. We're also continuing our investigation into the root cause of this issue.
Nov 25, 2024, 5:29 AM GMT+2
Nov 25, 2024, 5:00 AM GMT+2
Our automated systems alerted us to an issue in which some users may be intermittently unable to access their mailboxes in Exchange Online using any connection method or their calendar functionality in Microsoft Teams. We're analyzing a portion of Exchange Online infrastructure responsible for accessing mailboxes to understand the root cause of the issue and determine our next troubleshooting steps.