Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods

Timeline

Every update Microsoft posted for this issue, newest first.

1. Nov 13, 2026, 05:10 CET

   We’re continuing our efforts to improve server stability to improve traffic flow. This includes adjusting traffic protocols, redistributing traffic, and applying strategic traffic blocking measures.
   
   We're observing partial recovery across regions in which we've applied these adjustments; however, these actions aren't resulting in sustained recovery, so we're reviewing what additional actions we can take to improve overall infrastructure stability.

2. Nov 13, 2026, 04:34 CET

   As part of our investigation into the sustained traffic management imbalances, we’re reviewing traffic flows and affected infrastructure to identify opportunities to optimize routing. This includes verifying the reasons for service failures so we can develop specific actions to improve stability.
   
   We will continue to share more information as soon as we have it, and for now we can confirm that there is no indication this is the result of malicious activity. We’ll continue to apply learnings towards remediation actions as we confirm effectiveness mitigation actions.

3. Nov 13, 2026, 03:54 CET

   We’ve monitored the status of the changes applied to improve serviceability and confirmed that change is not taking as expected. We’re identifying alternate workstreams that can be applied to increase capacity in the face of sustained traffic management imbalances.

4. Nov 13, 2026, 03:09 CET

   We’re applying infrastructure capacity improvements where possible in an effort to help support traffic in regions coming online. We’re continuing to monitor the results of changes applied so we can identify strategic actions that can help to improve service health across all affected regions.

5. Nov 13, 2026, 02:45 CET

   We’re seeing positive results with our efforts to restart affected infrastructure. We’re actively monitoring the performance of these to verify stability which will support improved availability. Remediation actions will be expanded as we confirm stability with the changes applied.

6. Nov 13, 2026, 02:06 CET

   Our investigation has found that a process on the affected servers responsible for establishing secure connections becomes overwhelmed, causing the servers to stop processing requests. We're preparing a configuration change to address this behavior that can be applied across all affected servers, and we're validating it on a subset of servers before applying it more broadly alongside restarts of the affected infrastructure. In parallel, we've begun reverting a recent network configuration change that correlates with the start of impact and are monitoring to determine whether this contributes to recovery.
   
   The temporary traffic limitations we previously described are now in effect in specific locations. We're monitoring the affected servers in those locations to confirm whether they remain stable while handling a narrower set of connections, after which we'll gradually reintroduce additional traffic.

7. Nov 13, 2026, 00:59 CET

   While the servers we've returned to service initially remain healthy, we've observed that they can become unresponsive again once they begin receiving traffic. We're analyzing diagnostic data from these servers with our networking and platform experts to determine what's triggering this behavior.
   
   Building on the protective traffic management measures we've implemented, we're also temporarily limiting which types of traffic can reach the affected infrastructure in specific locations. This will help us determine whether a particular type of request is contributing to the impact and allow us to restore service incrementally. Additionally, we're rebuilding a subset of affected servers using a previous software configuration to validate whether this prevents them from becoming unresponsive, and we'll expand this approach to additional servers if we observe positive results.

8. Nov 12, 2026, 23:57 CET

   We've begun returning a portion of the affected servers to service, and they're remaining stable so far. We’ve also shifted traffic and connections to alternative pathways wherever possible and have observed limited recovery in some regions.
   
   We've streamlined our recovery process to expedite returning the remaining affected servers to service. To further support recovery, we're implementing protective traffic management measures in a specific location to reduce load on the affected infrastructure, and we'll expand these measures to additional locations if we observe positive results. As capacity is restored, users may experience a gradual recovery as their clients reconnect to the service.

9. Nov 12, 2026, 23:00 CET

   We’re continuing to pursue all available pathways to restore service, as our actions taken thus far have not provided the anticipated relief. Our investigation has found that a core process on the affected servers is becoming overwhelmed, which causes the servers to stop responding and contributes to the capacity loss.
   
   To validate a potential recovery approach, we're fully isolating a portion of our service infrastructure, restarting the affected components, and gradually reintroducing traffic to confirm our services remain stable before applying this approach more broadly. We're also analyzing traffic patterns across our entire service infrastructure and evaluating whether isolating traffic within each region may allow affected regions to recover independently.

10. Nov 12, 2026, 22:31 CET

    We're continuing to work through restarting and validating the affected servers to safely return them to service, and we're exploring opportunities to expedite this process. In parallel, we're assessing whether reverting the small number of recent configuration updates we identified could help accelerate recovery.

11. Nov 12, 2026, 21:56 CET

    We've validated an alternative health check method on a subset of affected infrastructure, which allowed the servers in that subset to successfully return to service, and we're now applying this change more broadly. We're also preparing an automated recovery process to continually detect and restart unresponsive servers, to help keep them in service while this change progresses. Additionally, our review of recent changes has identified a small number of configuration updates that we're investigating as potential contributors to the issue.

12. Nov 12, 2026, 21:38 CET

    While validating the targeted change, we found that many of the affected servers have become unresponsive, which is preventing us from confirming whether the change is effective. We're restarting these servers so they can come back online with the change in place, and we're applying the same approach to additional affected portions of our infrastructure to validate the results more broadly.

13. Nov 12, 2026, 20:57 CET

    While we haven't identified any recent changes that correlate with the start of impact, our investigation indicates the failed health checks may originate from a specific component on the affected servers that's responsible for processing them. We're deploying a targeted change to bypass this component on a subset of servers to validate whether this restores availability, and we've taken steps to prevent additional servers from being removed from service while we work to return the affected servers to service. We're also investigating why affected servers are experiencing elevated processor usage while handling requests.

14. Nov 12, 2026, 20:43 CET

    We've identified that affected servers are failing automated health checks, which is causing them to become unavailable, and this may be related to a recent change to a component involved in processing those checks. We're testing a configuration change on a subset of affected infrastructure to address this and, if successful, will apply it more broadly. In parallel, we've initiated a restart of all affected servers and are validating whether they're successfully returning to service.
    
    This quick update is designed to give the latest information on this issue.

15. Nov 12, 2026, 20:18 CET

    We've determined that the elevated load isn't driven by an overall increase in traffic, but by a large number of servers being unexpectedly unavailable, which is shifting load onto the remaining infrastructure. We're investigating what's causing these servers to become unavailable while we work to safely return them to service.
    
    This quick update is designed to give the latest information on this issue.

16. Nov 12, 2026, 20:06 CET

    We're aggressively pursuing all pathways to reduce impact. As a precaution, we've paused all deployments and configuration changes while we review recent changes for any correlation to this event. We've also moved traffic for some services off the affected infrastructure to further reduce load, with additional traffic moves in progress.
    
    This quick update is designed to give the latest information on this issue.

17. Nov 12, 2026, 19:57 CET

    We've completed redistributing Outlook connection traffic across our worldwide infrastructure, and we're moving additional traffic off the affected infrastructure to further reduce load. We're also restarting affected servers to return them to service. In parallel, we're investigating whether the elevated traffic reflects a genuine increase in requests or a shift in how traffic is being routed across our infrastructure.

18. Nov 12, 2026, 19:43 CET

    We've identified a pattern in which affected servers are becoming intermittently unavailable, which places additional strain on the remaining infrastructure and contributes to the connectivity issues users are experiencing. We've begun redistributing Outlook connection traffic across our broader worldwide infrastructure to help balance the load, which may result in some latency while this change is in effect, and we're reviewing recent changes to identify the source of the increased traffic.
    
    This quick update is designed to give the latest information on this issue.

19. Nov 12, 2026, 19:29 CET

    We've redirected a portion of traffic away from the affected infrastructure in the US to reduce load, and we're evaluating doing the same in other regions. While Exchange is the primarily impacted service, we've identified additional Microsoft 365 services that are also experiencing connectivity issues, and we're communicating those issues under MO1550821 on the Service Health Dashboard.
    
    This quick update is designed to give the latest information on this issue.

20. Nov 12, 2026, 19:19 CET

    Our investigation indicates that the affected infrastructure is experiencing elevated load across multiple regions, which is contributing to the connectivity errors users are receiving. We're restarting and repairing impacted portions of this infrastructure to mitigate impact and are evaluating options to redirect traffic to alternate infrastructure to expedite relief.

21. Nov 12, 2026, 18:45 CET

    We’ve identified connectivity errors occurring on a portion of Exchange Online infrastructure which receives and processes users’ access requests. We’ve collected networking logs to review to further investigate the source of these errors and confirm our next steps.

22. Nov 12, 2026, 17:55 CET

    We’re reviewing service health telemetry information to identify and isolate any errors contributing to impact for further investigation.

23. Nov 12, 2026, 17:20 CET

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