Microsoft is investigating Exchange Online issues under incident EX1464935 as of 16:01 UTC on 31 August 2026. User reports of Outlook send/receive problems are rising.
Confirmed within 13:12–16:12 UTC 31 Aug 2026: One new Microsoft 365 mail incident; no other listed-provider outages confirmed in the window.
Primary Symptom: Users are encountering significant delays or complete failures when sending or receiving new email messages through the Microsoft Outlook client and related mail flow pipelines.
Telemetry Analysis: Microsoft engineering teams are analyzing mail flow diagnostics and underlying service infrastructure telemetry to isolate the root cause.
Scope: Early reports indicate a sharp rise in user complaints on public outage platforms, though Microsoft has not yet specified which regional data centers or tenant subsets are carrying the bulk of the impact.
Do Not Alter Client Settings: Organizations are advised against modifying local DNS records, deleting Outlook profiles, or resetting user passwords, as emails are typically queued safely at the server level until mail flow is restored.
Aug 31, 2026 at 8:55 AM PDT
We are reviewing service telemetry and available information to determine if there is an issue happening and we'll update this message shortly with our latest findings. This communication serves as a preliminary notification about a potential issue affecting your service.
Aug 31, 2026 at 9:16 AM PDT
We're reviewing service telemetry and diagnostic data to isolate the source of the issue after receiving an increase in user-reported issues affecting Exchange Online. We'll keep refining the 'more info' section as additional impacts are identified.
Aug 31, 2026 at 9:33 AM PDT
We’ve isolated a common failure pattern across affected Exchange Online requests that is associated with authentication and protocol connectivity. We're analyzing service telemetry to identify the underlying source of impact and validate potential remediation options. Additionally, we’re continuing to assess the scope of impact and monitor for additional affected scenarios.
Aug 31, 2026 at 10:23 AM PDT
We've identified a potential corrective action for the affected infrastructure and are evaluating deployment options. We're monitoring service telemetry and affected Exchange Online transactions to determine whether the action is reducing impact and to better understand the scope of affected scenarios.
Aug 31, 2026 at 11:18 AM PDT
We're continuing to test our remediation strategy and in parallel we're working to confirm whether other services are impacted so we can expand our communications accordingly. This quick update is designed to give the latest information on this issue.
Aug 31, 2026 at 11:41 AM PDT
We're continuing to fine-tune our remediation strategy as our internal tests progress. We'll aim to provide an estimated time for remediation as soon as it's available.
Aug 31, 2026 at 12:43 PM PDT
We're continuing to perform comprehensive tests to ensure our mitigation strategy effectively resolves the issue without introducing additional impact. In parallel, we're exploring alternative remediation avenues to minimize impact in the interim.
Aug 31, 2026 at 1:36 PM PDT
We're reexamining recent changes made to the service to determine why the authentication components aren't being deployed as expected. Additionally, we are exploring every avenue to safely restore the components, including potentially reverting an update the affected infrastructure recently received. We're performing additional tests to evaluate the best course of action moving forward.
Aug 31, 2026 at 2:27 PM PDT
EX1464935 is still open as a service-degradation incident. Microsoft has not declared it resolved. The latest official update at 20:50 UTC points to a misconfiguration that is blocking authentication components from deploying on part of the infrastructure.
Aug 31, 2026 at 2:55 PM PDT
We're continuing our targeted review of affected infrastructure and recent changes made to the service to definitively confirm the cause of impact. We're additionally continuing to test and implement various mitigation strategies to apply the necessary authentication component, which have so far yielded positive results. We're monitoring these tests and mitigative actions closely and will provide an estimated time to resolution as soon as one is available. We understand the impact that events like these can have for your organization and we appreciate your patience as we work to mitigate this issue with the highest priority.
Aug 31, 2026 at 3:53 PM PDT
We're continuing to implement a targeted mitigation to re-apply core authentication components, and we're expanding this action more widely across the affected environments as we closely track the recovery of affected downstream scenarios. Users may notice gradual recovery to the scenarios identified in the "More info" section as our mitigation action takes effect in their corresponding sections of infrastructure, and we're continuing to review whether any additional actions may be required to achieve withstanding recovery across all affected scenarios. We'll provide an estimated time to resolution as soon as one is available.
Aug 31, 2026 at 4:33 PM PDT
We're expanding the aforementioned mitigation action more widely across the affected environments as we closely track the recovery of affected scenarios. Users should primarily begin to see gradual recovery to mail flow. Secondarily, and in parallel to the primary mitigation action previously described, we're restarting targeted sections of affected infrastructure to ensure the acceptance of the re-applied authentication components across affected services and aid the recovery of the downstream scenarios. This quick update is designed to give the latest information on this issue.
Aug 31, 2026 at 5:01 PM PDT
We're progressively restarting targeted sections of affected infrastructure to ensure the re-applied authentication components are effectively implemented across affected services. We expect this will aid the recovery of affected scenarios. Users should expect delayed delivery of backlogged messages and residual impact across downstream scenarios as these actions are continuing. We'll provide an expected recovery time as soon as one becomes available to us.
Aug 31, 2026 at 5:59 PM PDT
We’re seeing improvement across the affected environments as we observe the successful albeit gradual implementation of our mitigation actions. Users should expect to see varying degrees of recovery and residual delays until these actions have completed. We're closely monitoring the health of the service environment and will continue to aggressively pursue any available options to expedite our ongoing recovery work, and we'll provide an estimated recovery timeline as soon as one becomes available.
