Microsoft M365 issues

Microsoft has issued a service notice:
Some users may experience errors or failures when accessing their mailbox via any Exchange Online connection method.

Affected services: Exchange Online
Status: Service degradation
Issue type: Advisory
Start time: Sep 11, 2025, 8:50 AM CDT

User impact
Users may experience errors or failures when accessing their mailbox via any Exchange Online connection methods.

Scope of impact
Some users located in North America attempting to access their mailbox via any Exchange Online connection method may be impacted.

09/11/2025 12:40 PM - Now escalated as an incident for Microsoft.

09/11/2025 1:45 PM - Microsoft reports,”We’ve collected trace logs that indicate unexpectedly high resource utilization which may be contributing to connection errors and failures for mailboxes hosted on this portion of infrastructure. We’re currently working to identify and address the underlying cause of the high CPU utilization.”

09/11/2025 2:00 PM - Microsoft reports,”We’ve applied a configuration change to a portion of the impacted infrastructure and are seeing a reduction in some previously observed failures. We’re still reviewing system telemetry to assess if the impact of the configuration change on the overall resource utilization. If we observe a positive trend, we’ll deploy the configuration change broadly.”

09/11/2025 2:55 PM - Microsoft reports,”In addition to the configuration changes, we’re taking manual actions to stabilize the databases supporting the impacted infrastructure, which is expected to improve the overall service.”

09/11/2025 4:00 PM - Microsoft reports,”We’re continuing to monitor the configuration changes that were applied to the environment previously; however, we have not observed significant improvement. Subsequently, we’re manually applying additional incremental optimizations to improve database connections within the impacted environment, and we’re monitoring to confirm this improves service health.”

09/11/2025 5:20 PM - Microsoft reports, “We’re developing a change to override the build versioning errors that were observed in a subset of machines supporting the service. We’re also continuing to apply database optimizations in the impacted service environment to improve overall service quality.”

09/11/2025 9:00 PM - Microsoft reports, “Our optimization efforts continue to show stable increase in performance across affected environments as our change progresses. However, we’ve noted some portions of infrastructure that have plateaued slightly, and we’re troubleshooting to address the concerns. We’re analyzing additional options in these environments to further enhance restoration efforts and recover faster.”

09/12/2025 6:00 AM - Microsoft reports, “We’ve successfully completed our recovery mitigation and restored the majority of previously degraded infrastructure. Our monitoring of service health indicates that the service has returned to optimal levels. We’ll continue monitoring the environment over the course of the next several hours to ensure our services remain healthy. In tandem we’ll continue deployment of our build version updates, which we still expect to complete within the next six hours.

09/12/2025 6:00 AM - Our service health remains within expected thresholds as we continue our build versioning update. We’ll continue to provide updates on this deployment for the next several hours as it completes.”

09/12/2025 8:35 AM - Microsoft reports, “The service health across different connection methods remains stable and healthy. We’re continuing to roll out the build update across the remaining affected infrastructure and it is progressing as expected. We’ll maintain proactive monitoring of the environment and will implement targeted mitigations if needed to ensure continued service stability. We’ll provide an update earlier if there is a significant change in service health or progress in our remediation efforts.”

09/12/2025 1:00 PM - Microsoft reports, “The service has remained healthy as we’re actively monitoring telemetry and implementing proactive measures to maintain stability during peak traffic hours in the Americas region. In parallel, we’re working to accelerate the updated build deployment, intended to ensure full resolution, to affected infrastructure. We do not have an ETA for completion at this time. We’ll provide an update ahead of the next scheduled update if there is a significant change in service health or progress in our remediation efforts. Note that this will likely be the last update for today and next update in not scheduled till 9:30pm.”

09/15/2025 10:00 AM - Microsoft reports, “We’re continuing to monitor the deployment of the build and it is progressing as expected. In parallel, we’re closely reviewing stability across all connection methods to ensure the overall service health remains healthy.”

09/15/2025 10:00 AM - UWM will continue to monitor the Microsoft service and update as necessary for any changes.