Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods
Degraded Ongoing
- Started
- Ended
- Not yet
- Affects
- Exchange Online
Timeline (UK time)
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Additionally, on-prem mail flow may be affected if it goes to or from Exchange Online. Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current Status: We remain focused on addressing residual impact and ensuring reliable service restoration. We continue to assess recovery across various connection methods and closely monitor service health to verify sustained stability. At this time, we have no evidence of malicious activity associated with this incident. We will continue to treat this with urgency until full mitigation, and we will share a full Post-Incident Report with root cause and defense-in-depth actions after mitigation is complete. Next update by: Friday, November 13, 2026, at 6:00 PM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Additionally, on-prem mail flow may be affected if it goes to or from Exchange Online. Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current Status: We're observing sustained improvements in service availability as recovery progresses across affected Microsoft 365 services. While service functionality continues to improve, some users may still experience intermittent connectivity issues or delayed email delivery. Our efforts are increasingly focused on resolving the remaining issues and restoring consistent service for all affected users. We're validating recovery across different connection methods and monitoring service stability to confirm that improvements are sustained. At this time, we have no evidence of malicious activity associated with this incident. We will continue to treat this with urgency until full mitigation, and we will share a full Post-Incident Report with root cause and defense-in-depth actions after mitigation is complete. Next update by: Friday, November 13, 2026, at 4:00 PM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Additionally, on-prem mail flow may be affected if it goes to or from Exchange Online. Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current Status: We're continuing to see improvements in service availability, with email queues significantly reduced and approaching normal levels. Some users may still experience intermittent access issues or delayed email delivery as recovery continues. We've implemented additional mitigation measures and are restoring the remaining affected infrastructure while investigating residual service issues. We're closely monitoring service health and validating recovery across affected connection methods to ensure sustained service stability. At this time, we have no evidence of malicious activity associated with this incident. We will continue to treat this with urgency until full mitigation, and we will share a full Post-Incident Report with root cause and defense-in-depth actions after mitigation is complete. Next update by: Friday, November 13, 2026, at 3:00 PM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Additionally, on-prem mail flow may be affected if it goes to or from Exchange Online. Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current Status: We're seeing continued recovery progress across affected regions, with broader improvements now observed in North America and sustained improvements across much of Europe. We're also seeing encouraging recovery signals in Asia Pacific, although some users may continue to experience intermittent access issues or delayed email delivery as mitigation progresses across the remaining affected infrastructure. Our focus remains on stabilizing recovered infrastructure, completing mitigation in the remaining impacted areas, and reducing delayed email queues and backlogs. We're closely monitoring service consistency and validating recovery across different connection methods as we work toward full mitigation. At this time, we have no evidence of malicious activity associated with this incident. We will continue to treat this with urgency until full mitigation, and we will share a full Post-Incident Report with root cause and defense-in-depth actions after mitigation is complete. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 2:00 PM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Additionally, on-prem mail flow may be affected if it goes to or from Exchange Online. Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: We’re seeing encouraging recovery progress in Europe, with service availability and email delivery performance improving across a growing portion of affected Microsoft 365 infrastructure. Japan remains comparatively more stable, while North America is also improving; however, some users may still experience intermittent issues as recovery actions continue. We're focused on addressing the remaining areas of disruption and improving service consistency across affected regions. Reducing email queues and backlogs remains a priority, and the extended 48-hour email timeout window remains in place to help protect delayed messages as delivery catches up. At this time, we have no evidence of malicious activity associated with this incident. We will continue to treat this with urgency until full mitigation, and we will share a full Post-Incident Report with root cause and defense-in-depth actions after mitigation is complete. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 1:00 PM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Additionally, on-prem mail flow may be affected if it goes to or from Exchange Online. Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: We've made additional progress toward service recovery, with recovery actions completed across portions of the affected infrastructure in the Asia Pacific region. Traffic is being gradually restored, and we're seeing improvements in key customer scenarios, including mailbox access and delayed email processing. However, some users may continue to experience intermittent issues. Our focus is now on extending these recovery actions across affected infrastructure in other regions, while continuing stabilization efforts and adding supporting capacity to improve service consistency. Reducing email queues and backlogs remains a priority, and the extended 48-hour email timeout window remains in place to help protect delayed messages as delivery catches up. At this time, we have no evidence of malicious activity associated with this incident. We will continue to treat this with urgency until full mitigation, and we will share a full Post-Incident Report with root cause and defense-in-depth actions after mitigation is complete. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 12:00 PM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Additionally, on-prem mail flow may be affected if it goes to or from Exchange Online. Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: Recovery efforts are ongoing across impacted infrastructure. We are seeing early signs of stabilization, but service capacity has not yet returned to normal levels and health remains variable as traffic is carefully reintroduced. Our primary mitigation path continues to focus on service stability and controlled recovery. Engineering teams are cycling affected infrastructure through traffic drain, restart, remediation, and staged return-to-service while monitoring closely. We are also evaluating additional mitigation options to improve recovery speed and consistency. Network and traffic-management actions remain in progress, and we continue to prioritize backlog and queue health to preserve delayed mail during recovery. As part of this effort, we are extending the email timeout window to 48 hours to help protect delayed messages while service recovery continues. At this time, we are not aware of any malicious activity causing this incident. We will continue to treat this with urgency until full mitigation, and we will share a full Post-Incident Report with root cause and defense-in-depth actions after recovery is complete. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 10:00 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Additionally, on-prem mail flow may be affected if it goes to or from Exchange Online. Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: We’re continuing to see increased server capacity stability after applying the upstream authentication/routing configuration component patch. With confirmation of server stability across the portions of infrastructure to which we've applied the patch, we’ve initiated its expansion systematically to focus on infrastructure supporting regions currently within or entering peak business hours. We’ll continue to monitor the status of changes applied and develop additional modifications intended to improve server stability and capacity. As of now, we are not aware of any malicious activity that is causing this incident. We will continue to treat this incident with urgency and priority until full resolution. Once mitigated, we will provide full details of the root cause, defense-in-depth repair items, and more within a Post-Incident Report. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 9:00 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Additionally, on-prem mail flow may be affected if it goes to or from Exchange Online. Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: We’re seeing positive results for server stability after applying an upstream authentication/routing configuration component patch to a portion of our infrastructure. We’ll continue to monitor its progress and are working to expand it to servers supporting active regions coming online. As of now, we are not aware of any malicious activity that is causing this incident. We will continue to treat this incident with urgency and priority until full resolution. Once mitigated, we will provide full details of the root cause, defense-in-depth repair items, and more within a Post-Incident Report. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 8:30 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Additionally, on-prem mail flow may be affected if it goes to or from Exchange Online. Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: We’re continuing to monitor activity across regions to evaluate server status and determine actions that can be taken to improve capacity. This includes reviewing server performance and confirming that developed patches have been applied and working as intended after infrastructure reboots are completed. At this point, we have observed marginal success. In parallel, we’re taking action to expand capacity through the utilization of Virtual Machines. As of now, we are not aware of any malicious activity that is causing this incident. We will continue to treat this incident with urgency and priority until full resolution. Once mitigated, we will provide full details of the root cause, defense-in-depth repair items, and more within a Post-Incident Report. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 7:30 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Additionally, on-prem mail flow may be affected if it goes to or from Exchange Online. Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: As part of our ongoing efforts to advance the recoverability of our frontend servers, we’re evaluating traffic controls that can be applied to increase capacity and stability. This includes traffic optimization actions such as traffic throttling, protocol adjustments, and failover routing intended to improve stability in active regions. In parallel, were expanding internal testing to track activity within a contained environment to improve traffic monitoring and issue detection capabilities. As of now, we are not aware of any malicious activity that is causing this incident. We will continue to treat this incident with urgency and priority until full resolution. Once mitigated, we will provide full details of the root cause, defense-in-depth repair items, and more within a Post-Incident Report. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 7:30 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: We’re continuing to pursue multiple workstreams to pinpoint the underlying cause of the traffic influx and advance the recoverability of the backend servers. We’re taking a measured approach to identify and repair affected infrastructure to improve the ability to confirm the developed changes were applied. We’re tracking the results of this approach to verify the servers are showing the anticipated recovery and performance intended. As of now, we are not aware of any malicious activity that is causing this incident. We will continue to treat this incident with urgency and priority until full resolution. Once mitigated, we will provide full details of the root cause, defense-in-depth repair items, and more within a Post-Incident Report. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 7:00 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: We appreciate your organization’s patience and understanding while we work with urgency to resolve this incident. As we’ve applied our current ongoing mitigation actions, we’ve observed a surge in outbound call volume from our routing services to our backend servers. This occurs when the backend servers outbound service cannot properly route to the backend machines. We’re continuing to observe heightened volume due to traffic rebalancing actions that we have taken throughout this event. We’re working on multiple workstreams to pinpoint the underlying cause of this traffic influx and address it. Actions we're currently taking include scaling up virtual machines to increase capacity and reduce load. Additionally, we’re querying for machines in a bad state to perform a force sync for our recent network change, which may improve service availability. However, we are encountering issues with the machines being stuck in a bad state, preventing our changes from syncing as expected. We’ll continue to monitor the effectiveness of changes applied so we can determine what refinements are necessary. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 6:30 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 5:30 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 4:30 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 4:00 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 3:30 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 3:00 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 2:00 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 1:00 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Friday, November 13, 2026, at 12:00 AM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Thursday, November 12, 2026, at 11:00 PM UTC
- Degraded
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. Next update by: Thursday, November 12, 2026, at 10:00 PM UTC This quick update is designed to give the latest information on this issue.
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Thursday, November 12, 2026, at 10:00 PM UTC
- Degraded
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. Next update by: Thursday, November 12, 2026, at 9:00 PM UTC This quick update is designed to give the latest information on this issue.
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Impact to additional Microsoft 365 services is described under MO1550821 in the Service Health Dashboard. Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Thursday, November 12, 2026, at 9:00 PM UTC
- Degraded
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. Next update by: Thursday, November 12, 2026, at 8:00 PM UTC
- Degraded
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.
- Degraded
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.
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Thursday, November 12, 2026, at 8:00 PM UTC
- Degraded
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.
- Degraded
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.
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Thursday, November 12, 2026, at 7:30 PM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Current status: 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. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Thursday, November 12, 2026, at 8:00 PM UTC
- Degraded
Title: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods User impact: Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods. More info: Potentially impacted connection methods may include: - Outlook on the web - Messaging API (MAPI) - Exchange ActiveSync (EAS) - Representational State Transfer (REST) API Current status: We’re reviewing service health telemetry information to identify and isolate any errors contributing to impact for further investigation. Scope of impact: This issue may affect users attempting to access their mailbox in Exchange Online using the affected connection methods. Next update by: Thursday, November 12, 2026, at 6:00 PM UTC
- Degraded
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.
Wording above is from Microsoft 365 service health. Original notice.