Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: We've deployed a fix that has relieved issue for the majority of impacted users and we’re continuing to monitor the rollout of this fix while also investigating the subset of users still experiencing impact. We'll provide a timeline for full mitigation of this impact by our next scheduled update.

Scope of impact: This issue appears to be intermittently impacting a small subset of users, though potentially any user accessing Exchange Online may be intermittently affected.

Root cause: An indexing issue within a section of mailbox database infrastructure responsible for providing access to Exchange Online mailboxes caused mailbox state invalidations and client disconnections, resulting in impact.

Next update by: Tuesday, November 25, 2025, at 9:30 PM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: From our analysis into the service health telemetry errors and reports of impact from a subset of users, we suspect there may be a code issue within the affected service infrastructure that’s contributing to the persistent impact. We’re investigating further into this potential code issue to pinpoint what’s causing the behavior and to identify a solution that addresses the remaining impact.

Scope of impact: This issue appears to be intermittently impacting a small subset of users, though potentially any user accessing Exchange Online may be intermittently affected.

Root cause: An indexing issue within a section of mailbox database infrastructure responsible for providing access to Exchange Online mailboxes caused mailbox state invalidations and client disconnections, resulting in impact.

Next update by: Monday, November 24, 2025, at 9:30 PM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: While many users gave feedback that the impact has been resolved for them, some may experience persisting impact. Our analysis into the remaining impact is ongoing, and we're analyzing service health telemetry errors in conjunction with reports of impact from a subset of users to identify why our solution hasn't fully resolved this issue for them.

Scope of impact: This issue appears to be intermittently impacting a small subset of users, though potentially any user accessing Exchange Online may be intermittently affected.

Root cause: An indexing issue within a section of mailbox database infrastructure responsible for providing access to Exchange Online mailboxes caused mailbox state invalidations and client disconnections, resulting in impact.

Next update by: Saturday, November 22, 2025, at 2:00 AM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: While some users have reported recovery after we applied the changes to correct the indexing issue, we've received reports from some users that impact persists. We're continuing to review to identify if it's relating to the indexing issue or whether other factors may be contributing to the impact.

Scope of impact: This issue appears to be intermittently impacting a small subset of users, though potentially any user accessing Exchange Online may be intermittently affected.

Root cause: An indexing issue within a section of mailbox database infrastructure responsible for providing access to Exchange Online mailboxes caused mailbox state invalidations and client disconnections, resulting in impact.

Next update by: Friday, November 21, 2025, at 10:00 PM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: We've received confirmation from some users stating that they experience remediation. We're continuing to await further verification from more impacted users to confirm that the issue is fixed.

Scope of impact: This issue appears to be intermittently impacting a small subset of users, though potentially any user accessing Exchange Online may be intermittently affected.

Start time: Friday, November 20, 2025, at 1:25 PM UTC

Root cause: An indexing issue within a section of mailbox database infrastructure responsible for providing access to Exchange Online mailboxes caused mailbox state invalidations and client disconnections, resulting in impact.

Next update by: Friday, November 21, 2025, at 5:30 PM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: We've identified that an indexing issue within a section of mailbox database infrastructure responsible for providing access to Exchange Online mailboxes caused mailbox state invalidations and client disconnections, resulting in impact. We've corrected the indexing issue within the affected infrastructure and are awaiting verification from some impacted users to confirm if the issue is mitigated.

Scope of impact: This issue appears to be intermittently impacting a small subset of users, though potentially any user accessing Exchange Online may be intermittently affected.

Root cause: An indexing issue within a section of mailbox database infrastructure responsible for providing access to Exchange Online mailboxes caused mailbox state invalidations and client disconnections, resulting in impact.

Next update by: Friday, November 21, 2025, at 1:30 PM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: Our analysis so far has identified some connectivity issues and backlogs of requests. While our investigation to identify the precise origin of these issues is ongoing, we've applied some changes to the service which appear to have had a positive effect on service health. We're continuing to investigate to identify the underlying root cause of impact and construct a long-term fix solution.

Scope of impact: This issue appears to be intermittently impacting a small subset of users, though potentially any user accessing Exchange Online may be intermittently affected.

Next update by: Friday, November 21, 2025, at 10:30 AM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: Our investigation into the CPU utilization on the affected databases is delayed due to an unrelated issue accessing logs specific to the errors. We're working to resolve the access issue and continue the root cause investigation.

Scope of impact: This issue appears to be intermittently impacting a small subset of users in customer tenants, though potentially any user access Exchange Online may be intermittently affected.

Next update by: Friday, November 21, 2025, at 1:30 AM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: Our analysis of provided logs and telemetry indicates that some databases that facilitate Exchange Online mailbox access are experiencing excessive CPU utilization causing some requests to fail, resulting in impact. We're expanding our investigation to identify the specific processes responsible for impact and determine a mitigation strategy.

Scope of impact: This issue appears to be intermittently impacting a small subset of users in customer tenants, though potentially any user access Exchange Online may be intermittently affected.

Next update by: Thursday, November 20, 2025, at 11:30 PM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: We're continuing our analysis of provided logs to assist in the investigation and isolate the underlying cause of impact.

Scope of impact: Your organization is impacted by this event, and a subset of users are unable to access their mailbox through all Exchange Online connection methods.

Next update by: Thursday, November 20, 2025, at 11:00 PM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: We reviewed the error codes and suspect that the issue is related to specific API calls failing. We're reviewing the affected API calls and whether there have been any recent changes to better understand the source of the errors, which will help us determine our next troubleshooting steps.

Scope of impact: Your organization is impacted by this event, and a subset of users are unable to access their mailbox through all Exchange Online connection methods.

Next update by: Thursday, November 20, 2025, at 8:30 PM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: We’ve identified that 500-error codes are being returned in the HAR traces provided by your representatives. We're further investigating the source of the error codes to help with isolating the root cause.

Scope of impact: Your organization is impacted by this event, and a subset of users are unable to access their mailbox through all Exchange Online connection methods.

Next update by: Thursday, November 20, 2025, at 7:00 AM UTC

Title: Some users may be intermittently unable to access their Exchange Online mailboxes using any connection method

User impact: Users may be intermittently unable to access their Exchange Online mailboxes using any connection method.

Current status: We’ve received reports from your organization that a subset of users are unable to access their mailbox through any Exchange Online connection method. We're reviewing HTTP Archive format (HAR) traces and error logs to isolate the cause of this problem and determine an appropriate remediation action.

Scope of impact: Your organization is impacted by this event, and a subset of users are unable to access their mailbox through all Exchange Online connection methods.

Next update by: Thursday, November 20, 2025, at 3:00 AM UTC