Some users may be unable to search for email in Outlook desktop and Outlook on the web

Title: Some users may be unable to search for email in Outlook desktop and Outlook on the web User impact: Users may have been unable to search for email in Outlook desktop and Outlook on the web. Final status: We've validated through our extended monitoring that the errors associated with impact have not reoccurred and confirmed that impact is remediated. Scope of impact: Some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web may have been impacted. Start time: Friday, September 18, 2026, at 2:36 AM UTC End time: Thursday, October 1, 2026, at 7:01 PM UTC Root cause: The portion of service infrastructure responsible for facilitating the Outlook search was receiving increased request traffic preventing the service from being able to handle the traffic in an efficient manner, causing impact. Next steps: - We've deployed our remediation to all environments to ensure that this issue does not reoccur. - We're continuing to optimize our response to user needs by prioritizing important feature adaptations and improvements.

Title: Some users may be unable to search for email in Outlook desktop and Outlook on the web User impact: Users may be unable to search for email in Outlook desktop and Outlook on the web. Current status: As we continue to monitor the progress of our deployment, we've observed that the occurrences of the error code generated by this issue have dropped significantly. We're conducting a period of extended monitoring to validate this trend and ensure remediation. Scope of impact: Some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web may be impacted. This information may be updated as our investigation continues. Root cause: The portion of service infrastructure responsible for facilitating the Outlook search is receiving increased request traffic, which is preventing the service from being able to handle the traffic in an efficient manner and is causing impact. Next update by: Friday, October 2, 2026, at 2:30 AM UTC

Title: Some users may be unable to search for email in Outlook desktop and Outlook on the web User impact: Users may be unable to search for email in Outlook desktop and Outlook on the web. Current status: We've observed positive trends in telemetry after deploying our fix for this issue and are continuing to monitor to ensure full remediation for all affected users. Scope of impact: Some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web may be impacted. This information may be updated as our investigation continues. Root cause: The portion of service infrastructure responsible for facilitating the Outlook search is receiving increased request traffic, which is preventing the service from being able to handle the traffic in an efficient manner and is causing impact. Next update by: Friday, October 2, 2026, at 12:30 AM UTC

Title: Some users may be unable to search for email in Outlook desktop and Outlook on the web User impact: Users may be unable to search for email in Outlook desktop and Outlook on the web. Current status: Our deployment of configuration changes to remediate impact is continuing and taking slightly longer to fully saturate than anticipated. We'll continue to monitor its deployment and provide an updated remediation timeline as soon as one becomes available. Scope of impact: Some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web may be impacted. This information may be updated as our investigation continues. Root cause: The portion of service infrastructure responsible for facilitating the Outlook search is receiving increased request traffic, which is preventing the service from being able to handle the traffic in an efficient manner and is causing impact. Next update by: Thursday, October 1, 2026, at 8:00 PM UTC

Title: Some users may be unable to search for email in Outlook desktop and Outlook on the web User impact: Users may be unable to search for email in Outlook desktop and Outlook on the web. Current status: Our investigation into the source of the increased request traffic is ongoing. In parallel, our deployment of configuration changes to remediate impact is continuing, and we anticipate it will complete, resolving impact for all users, by our next scheduled communication update. Scope of impact: Some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web may be impacted. This information may be updated as our investigation continues. Root cause: The portion of service infrastructure responsible for facilitating the Outlook search is receiving increased request traffic, which is preventing the service from being able to handle the traffic in an efficient manner and is causing impact. Next update by: Tuesday, September 29, 2026, at 8:00 PM UTC

Title: Some users may be unable to search for email in Outlook desktop and Outlook on the web User impact: Users may be unable to search for email in Outlook desktop and Outlook on the web. Current status: Our current understanding of the impact suggests that the portion of service infrastructure responsible for facilitating the Outlook search is receiving increased request traffic, which is preventing the service from being able to handle the traffic in an efficient manner. We're continuing to investigate the reason for the increased traffic while our deployment of the aforementioned configuration changes is ongoing. Scope of impact: Some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web may be impacted. This information may be updated as our investigation continues. Root cause: The portion of service infrastructure responsible for facilitating the Outlook search is receiving increased request traffic, which is preventing the service from being able to handle the traffic in an efficient manner and is causing impact. Next update by: Monday, September 28, 2026, at 9:30 PM UTC

Title: Some users may be unable to search for email in Outlook desktop and Outlook on the web User impact: Users may be unable to search for email in Outlook desktop and Outlook on the web. Current status: We're continuing to deploy a set of configuration changes that we anticipate might remediate impact while gathering more information to validate our root cause hypothesis. Scope of impact: Some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web may be impacted. This information may be updated as our investigation continues. Next update by: Saturday, September 26, 2026, at 3:30 AM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: Our analysis into the behavior of mailbox queries has identified a potential source of this issue. We're gathering more information to validate our hypothesis in tandem with deploying a set of configuration changes we anticipate can remediate the impact. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Friday, September 25, 2026, at 10:00 PM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: We’ve determined that additional configuration changes are required to further mitigate impact. We’re applying these changes across the affected infrastructure and monitoring the affected service to validate successful remediation. In parallel, we’re continuing our investigation to isolate and validate the underlying cause of this issue. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Friday, September 25, 2026, at 3:00 AM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: We've applied configuration changes to allow user queries to consume more memory across applicable mailbox or container types. We're conducting a period of monitoring to verify its success in mitigating impact and to validate the underlying root cause of impact. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Thursday, September 24, 2026, at 7:30 PM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: During our extended period of monitoring, we received additional reports from some users indicating that they're also impacted. We're analyzing these additional reports while in parallel, working to identify the underlying root cause of the search issues. Previously affected users whose mailboxes have been rerouted to alternate infrastructure should still no longer be experiencing impact. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Thursday, September 24, 2026, at 9:00 AM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: We've finished routing the remaining affected mailboxes to alternate healthy infrastructure, and we've received feedback from a subset of the affected users that the issue is no longer occurring. We're monitoring service health telemetry to validate if any additional remediation actions are required to restore full service functionality. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Thursday, September 24, 2026, at 4:00 AM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: We've completed processing the remaining mailbox moves and we're performing validation checks to confirm if impact is now resolved or if any further mitigation actions are required. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Wednesday, September 23, 2026, at 5:00 PM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: We're continuing to process the remaining mailbox moves and estimate that this should be complete by our next scheduled update. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Wednesday, September 23, 2026, at 3:00 PM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: The aforementioned fix didn’t provide the expected recovery. We’ve since confirmed that relocating affected mailboxes to alternate database infrastructure restores search functionality, and most of these moves have now been completed. The remaining mailbox moves are in progress, and we’re monitoring the results to confirm that this mitigation fully resolves the impact, with completion expected by our next scheduled update. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Wednesday, September 23, 2026, at 1:00 PM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: While we continue our analysis of the aforementioned exceptions relating to an invalid authentication component so we can refine our understanding of the underlying cause of impact, we’re in the process of deploying an expedited fix to circumvent the resource allocation limits within affected mailboxes. We anticipate that these actions will further our clarification on the needed troubleshooting steps to ensure that impact is fully resolved. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Wednesday, September 23, 2026, at 10:00 AM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: We're reviewing our service side logs to identify the reason that the resource allocation limit is being hit, so that we can develop a mitigation strategy to relieve the impact. In tandem, we've isolated exceptions relating to an invalid authentication component and are investigating these to determine whether they're contributing to this issue. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Wednesday, September 23, 2026, at 3:30 AM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: As we finalize our investigation into whether a resource allocation issue may be contributing to the impact, we're proceeding with further analysis of the exceptions associated with impact to better understand their source and develop our next steps. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Tuesday, September 22, 2026, at 8:00 PM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: Our investigation of the section of mailbox database infrastructure is ongoing, and we're focusing our efforts on determining whether an issue with resource allocation is the underlying root cause before we begin developing a mitigation strategy. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Tuesday, September 22, 2026, at 4:00 AM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: We’ve isolated the search failures to resource constraints affecting search processing within a section of mailbox database infrastructure. We’re assessing the health and resource allocation of the affected infrastructure to determine why these limits are being reached and identify our next troubleshooting actions. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Friday, September 18, 2026, at 6:00 PM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: We’re further pursuing or analysis into the system logs to refine our understanding of where the search issues are manifesting as these actions will expedite the development of our next troubleshooting actions. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Friday, September 18, 2026, at 2:00 PM UTC

Title: Some users are unable to search for email in Outlook desktop and Outlook on the web User impact: Users are unable to search for email in Outlook desktop and Outlook on the web. Current status: We're analyzing system logs to understand the source of the search issues, which will help us determine our next troubleshooting steps. Scope of impact: Your organization is affected by this event, and the issue impacts some users attempting to search for Exchange Online email in the Outlook desktop client and Outlook on the web. This information may be updated as our investigation continues. Next update by: Friday, September 18, 2026, at 7:30 AM UTC

Title: Some users are unable to search for email in Outlook and Outlook on the web User impact: Users are unable to search for email in Outlook and Outlook on the web. Current status: We're investigating a potential issue with Exchange Online and checking for impact to your organization. We'll provide an update within 30 minutes.