Users may be unable to access their mailbox using any Exchange Online connection method

Title: Users may be unable to access their mailbox using any Exchange Online connection method

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

More info: Additionally, some affected users may experience delays sending and receiving email messages or may experience log in failures as part of this issue.

Current status: We're actively monitoring service availability following our manual mitigation measures, which have led to a steady improvement in stability. Simultaneously, we’re prioritizing the development of a comprehensive fix to resolve the root cause.

Scope of impact: Any user may be impacted when attempting to access their mailbox using any Exchange Online connection method.

Root cause: A multi-layered caching issue within our processing infrastructure generated excessive requests to backend components. This led to high resource utilization, which in turn caused mailbox access issues for end users.

Start time: Thursday, July 10, 2025, at 7:00 PM UTC

Next update by: Saturday, July 12, 2025, at 8:00 AM UTC

Title: Users may be unable to access their mailbox using any Exchange Online connection method

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

More info: Additionally, some affected users may experience delays sending and receiving email messages, or may experience log in failures as part of this issue.

Current status: We’re continuing our recovery efforts and are pursuing parallel pathways to fully resolve this issue.

To mitigate impact to users as quickly as possible, we’re adding additional database capacity within the affected infrastructure. We’re seeing steady improvements to service availability within our telemetry as this process continues. While this work is underway, we’re preparing a code fix to address the underlying cause of impact and fully remediate the problem. We anticipate that the remaining impacted users will see improvements in service availability as we complete these recovery steps.


Scope of impact: Any user may be impacted when attempting to access their mailbox using any Exchange Online connection method.

Root cause: A multi-layered caching issue within our processing infrastructure generated excessive requests to backend components. This led to high resource utilization, which in turn caused mailbox access issues for end users.

Start time: Thursday, July 10, 2025, at 7:00 PM UTC

Next update by: Saturday, July 12, 2025, at 2:00 AM UTC

We’ve added additional database capacity to help expedite mitigation of this issue and our telemetry is showing positive service health improvements for most users; however, some portions of our infrastructure are still operating below optimal levels. We’re working to recover service health for users hosted in those remaining sections of our service infrastructure.

This quick update is designed to give the latest information on this issue.

Title: Users may be unable to access their mailbox using any Exchange Online connection method

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

Current status: We’ve deployed a caching configuration change to the impacted environment to potentially remediate the impact and we’re validating to confirm whether we’re seeing positive signs of recovery to service health, which will determine our next troubleshooting steps. Additionally, we’re continuing our efforts to recover the impacted subset of service infrastructure to fully resolve the issue.

Scope of impact: Any user may be impacted when attempting to access their mailbox using any Exchange Online connection method.

Start time: Thursday, July 10, 2025, at 7:00 PM UTC

Next update by: Friday, July 11, 2025, at 11:00 PM UTC

Title: Users may be unable to access their mailbox using any Exchange Online connection method

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

Current status: We’re continuing our investigation into the cache configurations in the impacted environment and analyzing the affected subset of service infrastructure to further our understanding of the underlying cause of this issue. Though the root cause investigation is ongoing, we’re testing potential mitigative changes to remediate the impact as soon as possible.

Scope of impact: Any user may be impacted when attempting to access their mailbox using any Exchange Online connection method.

Start time: Thursday, July 10, 2025, at 7:00 PM UTC

Next update by: Friday, July 11, 2025, at 8:00 PM UTC

Title: Users may be unable to access their mailbox using any Exchange Online connection method

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

Current status: We're seeing continued impact after applying some infrastructure optimizations. We’re analyzing the cache configuration and authentication behavior in the affected environment to determine the underlying issue and identify the quickest path to remediate the impact.

Scope of impact: Any users may be impacted when attempting to access their mailbox using any Exchange Online connection method.

Start time: Thursday, July 10, 2025, at 7:00 PM UTC

Next update by: Friday, July 11, 2025, at 6:00 PM UTC

Title: Users may be unable to access their mailbox using any Exchange Online connection method

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

Current status: We're optimizing performance and traffic management on the affected infrastructure, to remediate impact.

Scope of impact: Any users may be impacted when attempting to access their mailbox using any Exchange Online connection method.

Start time: Thursday, July 10, 2025, at 7:00 PM UTC

Next update by: Friday, July 11, 2025, at 4:00 PM UTC

Title: Users may be unable to access their mailbox using any Exchange Online connection method

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

Current status: Our analysis of the portion of infrastructure responsible for traffic flow shows that requests aren’t being processed in an orderly fashion. We're working to determine whether this behavior is the root cause or a symptom, so we can identify the best path forward to help alleviate impact.

Scope of impact: Any users may be impacted when attempting to access their mailbox using any Exchange Online connection method.

Start time: Thursday, July 10, 2025, at 7:00 PM UTC

Next update by: Friday, July 11, 2025, at 9:00 AM UTC

Title: Users may be unable to access their mailbox using any Exchange Online connection method

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

Current status: We've identified that a portion of infrastructure responsible for the traffic flow may not be performing at expected thresholds. We're analyzing the telemetry from the infrastructure to validate if this is the root cause and determine the necessary mitigating actions.

Scope of impact: Any users may be impacted when attempting to access their mailbox using any Exchange Online connection method.

Start time: Thursday, July 10, 2025, at 7:00 PM UTC

Next update by: Friday, July 11, 2025, at 4:00 AM UTC

Title: Users may be unable to access their mailbox using any Exchange Online connection method

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

Current status: We're analyzing the service health telemetry in an effort to pinpoint the origin of impact.

Scope of impact: Any users located in Australia may be impacted when attempting to access their mailbox using any Exchange Online connection method.

Start time: Thursday, July 10, 2025, at 7:00 PM UTC

Next update by: Friday, July 11, 2025, at 2:00 AM UTC

Title: Potential issues accessing mailboxes via one or more connection methods

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

Current status: We're investigating a potential issue and checking for impact to your organization. We'll provide an update within 60 minutes.