Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

Title: Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

User impact: Users may have been unable to search mailbox or Address Book content in Exchange Online across connection methods.

Final status: We've completed deployment of our fix to resolve the authentication issue and validated with a subset of affected users that our fix successfully remediated impact.

Scope of impact: Some users attempting to search mailbox or Address Book content in Exchange Online across connection methods may have been affected.

Start time: Saturday, September 19, 2026, at 3:00 AM UTC

End time: Wednesday, September 30, 2026, at 4:00 PM UTC

Root cause: An authentication issue was preventing users from searching mailbox or Address Book content in Exchange Online.

Next steps:
- We're isolating how the authentication issue was introduced into our service to validate what additional actions we can take to ensure similar impact scenarios don't occur in the future.

This is the final update for the event.

Title: Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

User impact: Users may be unable to search mailbox or Address Book content in Exchange Online across connection methods.

Current status: The fix has begun deployment in the affected environment, and it appears to be remediating impact. This confirms that an authentication issue is preventing users from searching mailbox or Address Book content in Exchange Online. We’ll provide an estimated timeline for the complete saturation of this fix if it becomes available.

Scope of impact: Some users attempting to search mailbox or Address Book content in Exchange Online across connection methods may be affected. This section may be updated as our investigation progresses.

Root cause: An authentication issue is preventing users from searching mailbox or Address Book content in Exchange Online.

Next update by: Friday, October 2, 2026, at 9:00 PM UTC

Title: Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

User impact: Users may be unable to search mailbox or Address Book content in Exchange Online across connection methods.

Current status: We're continuing the development and validation of our potential fix, and an estimated timeline for their deployment will be provided if it becomes available.

Scope of impact: Some users attempting to search mailbox or Address Book content in Exchange Online across connection methods may be affected. This section may be updated as our investigation progresses.

Next update by: Tuesday, September 29, 2026, at 9:00 PM UTC

Title: Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

User impact: Users may be unable to search mailbox or Address Book content in Exchange Online across connection methods.

Current status: As we progress with our root cause analysis and validate the source for this event, we've determined that our potential fix will require some adjustments ahead of deployment. We're developing and validating these additions, and an estimated timeline for their deployment is expected to be available by our next scheduled communication update.

Scope of impact: Some users attempting to search mailbox or Address Book content in Exchange Online across connection methods may be affected. This section may be updated as our investigation progresses.

Next update by: Monday, September 28, 2026, at 9:00 PM UTC

Title: Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

User impact: Users may be unable to search mailbox or Address Book content in Exchange Online across connection methods.

Current status: We're preparing our potential fix for deployment to resolve the 503 errors and anticipate that deployment should be ready by the time of our next update.

Scope of impact: Some users attempting to search mailbox or Address Book content in Exchange Online across connection methods may be affected. This section may be updated as our investigation progresses.

Next update by: Sunday, September 27, 2026, at 9:00 PM UTC

Title: Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

User impact: Users may be unable to search mailbox or Address Book content in Exchange Online across connection methods.

Current status: We're developing and validating a potential fix to resolve an increase in 503 errors seen within our service processors and remediate impact.

Scope of impact: Some users attempting to search mailbox or Address Book content in Exchange Online across connection methods may be affected. This section may be updated as our investigation progresses.

Next update by: Saturday, September 26, 2026, at 9:00 PM UTC

Title: Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

User impact: Users may be unable to search mailbox or Address Book content in Exchange Online across connection methods.

Current status: We've completed performance optimizations on a subset of affected Exchange Online service infrastructure and validated that some affected users are seeing remediation, though impact is ongoing for others. We're implementing additional performance optimizations while we continue our investigation into the underlying root cause.

Scope of impact: Some users attempting to search mailbox or Address Book content in Exchange Online across connection methods may be affected. This section may be updated as our investigation progresses.

Next update by: Friday, September 25, 2026, at 8:30 PM UTC

Title: Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

User impact: Users may be unable to search mailbox or Address Book content in Exchange Online across connection methods.

Current status: We're initiating performance optimizations on a subset of affected Exchange Online service infrastructure to alleviate some impact while we continue to troubleshoot and isolate the underlying root cause.

Scope of impact: Some users attempting to search mailbox or Address Book content in Exchange Online across connection methods may be affected. This section may be updated as our investigation progresses.

Next update by: Thursday, September 24, 2026, at 10:30 PM UTC

Title: Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

User impact: Users may be unable to search mailbox or Address Book content in Exchange Online across connection methods.

Current status: We've validated that a subset of affected users are still experiencing impact at this time. We're analyzing the service infrastructure hosting affected mailboxes to isolate potential discrepancies leading to continued impact and to determine our next troubleshooting steps.

Scope of impact: Some users attempting to search mailbox or Address Book content in Exchange Online across connection methods may be affected. This section may be updated as our investigation progresses.

Next update by: Thursday, September 24, 2026, at 8:30 PM UTC

Title: Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

User impact: Users may be unable to search mailbox or Address Book content in Exchange Online across connection methods.

Current status: Our review of the service telemetry has led us to suspect that a portion of Exchange Online service infrastructure that facilitates the authentication flow necessary for searching for mailbox or Address Book content may be encountering failures. We've restarted the affected portion of infrastructure and are reaching out to some affected users to confirm whether this action has resolved the issue.

Scope of impact: Some users attempting to search mailbox or Address Book content in Exchange Online across connection methods may be affected. This section may be updated as our investigation progresses.

Next update by: Thursday, September 24, 2026, at 6:00 PM UTC

Title: Some users may be unable to search mailbox or Address Book content in Exchange Online across connection methods

User impact: Users may be unable to search mailbox or Address Book content in Exchange Online across connection methods.

Current status: We've received support cases indicating that some users can't search mailbox or Address Book content in Exchange Online across connection methods. We're reviewing our service telemetry to isolate the root cause of impact and develop a remediation strategy.

Scope of impact: Some users attempting to search mailbox or Address Book content in Exchange Online across connection methods may be affected. This section may be updated as our investigation progresses.

Next update by: Thursday, September 24, 2026, at 1:00 AM UTC