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: Due to our earlier mitigation efforts, users are no longer experiencing impact, however, our ongoing work described below is necessary to address the underlying issue and ensure the service remains stable.

Current status: We’re continuing to closely monitor the service availability and can confirm the fix remained effective during peak European hours. With this validation, we’re beginning the process to deploy the solution throughout the affected infrastructure.

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

Preliminary 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.

Next update by: Tuesday, July 15, 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 through our validation phase and closely monitoring service telemetry to confirm the fix is effective during European peak traffic. After validation, we will start the deployment. Thank you for your patience while we continue the work to 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

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.

Next update by: Tuesday, July 15, 2025, at 5:00 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 validation phase is ongoing, and our service availability remains healthy, with majority of users in a mitigated state. Once we finalize this validation phase, we’ll begin our deployment process. We appreciate your patience as we work towards full resolution of the underlying root cause.

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

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.

Next update by: Tuesday, July 15, 2025, at 10:30 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 completed our testing and have moved into our validation phase. We anticipate this validation phase may take some time complete; however most users should no longer be impacted while it progresses. Once validation is finalized, we’ll proceed with deployment and provide regular updates until we consider impact fully remediated.

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

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.

Next update by: Tuesday, July 15, 2025, at 5:00 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 continue to see service availability recover for the subset of infrastructure servicing users in Germany following our actions to increase database capacity. We expect testing for our new fix to complete by Monday, July 14, 2025, at 11:00 PM UTC, at which point we will prepare for deployment.

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

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.

Next update by: Tuesday, July 15, 2025, at 12:00 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 investigating reports of continued impact from users in Germany and found a portion of infrastructure that was missed when deploying our initial mitigation steps. We’ve created a new fix to include the missing portion of infrastructure and are testing to confirm it will resolve the issue. Concurrently, we’re adding additional database capacity within the affected infrastructure and we’re seeing service availability recover within our telemetry.

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

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.

Next update by: Monday, July 14, 2025, at 5:30 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: The fix to resolve the underlying cause of impact saturated 71 percent of the affected infrastructure, and service availability remains healthy. Out of an abundance of caution, we’ve intentionally slowed down the rollout to ensure there are no disruptions during peak business hours. Based on our telemetry, we’ve seen no further impact since our initial mitigation steps were completed. We’ll continue to closely monitor the service for any variances until the underlying issue is resolved.

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

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.

Next update by: Monday, July 14, 2025, at 5:30 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: The fix has reached 60 percent saturation, and we remain on track to reach 95 percent saturation by Monday, July 14, 2025, at 9:00 AM UTC.

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

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.

Next update by: Monday, July 14, 2025, at 10:30 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 confirmed the targeted deployment successfully resolved impact for the subset of infrastructure and started deploying the solution broadly to the rest of the affected infrastructure. The deployment is 28 percent saturated, and we expect this to reach 95 percent saturation by Monday, July 14, 2025, at 9:00 AM UTC.

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

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.

Next update by: Monday, July 14, 2025, at 2:30 AM UTC

We’ve started a targeted deployment of the solution to a subset of the affected infrastructure that experienced higher levels of impact. We’re testing to confirm it fully resolves the issue prior to deploying the solution throughout the rest of the affected 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: The process of preparing the fix for the broader deployment is progressing, though taking longer than initially anticipated. We expect the deployment will start before our next scheduled update. Once the broad fix deployment starts, we expect it will reach 95 percent saturation within 24 hours. We’ll provide a more precise estimated completion time once we begin the deployment.

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

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.

Next update by: Sunday, July 13, 2025, at 5:30 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’ve successfully deployed our fix to our internal infrastructure and validated that it fully resolves impact as expected. We’re initializing the broader deployment of this fix, which we anticipate will be ready to begin by our next update. We'll subsequently monitor its saturation throughout the affected environment, and we'll provide an estimated completion time as it becomes available.

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

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.

Next update by: Sunday, July 13, 2025, at 4:30 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 completed our pre-deployment steps and will be deploying and validating the fix within our internal infrastructure. We expect we’ll be able to start deploying throughout the affected infrastructure by our next scheduled update.
Service availability remains healthy, and we’ll continue to monitor the service for any changes until the underlying issue is remediated.

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

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.

Next update by: Sunday, July 13, 2025, at 1:30 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: Our fix to address the underlying cause of impact is now ready to be deployed internally for validation, which will then be rolled out through the affected infrastructure for complete mitigation.
In the meantime, overall service availability remains healthy and stable, after the manual mitigation steps implemented earlier.
We will continue to closely monitor the service and implement appropriate mitigation measures as needed to maintain service integrity until the underlying issue is fully resolved.

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 7:00 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.

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’ve confirmed based on our service health telemetry and confirmation from customers, that the majority of users are experiencing relief. We’re finalizing our comprehensive fix to address the underlying cause of impact, which we anticipate taking a few hours to complete, after which we’ll start our internal validation phase prior to deployment.

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 1:00 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.

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.