Microsoft is currently investigating Issue ID EX1464935, a service incident affecting Exchange Online that may cause users to experience email delivery failures, delays, and authentication-related issues when accessing Microsoft 365 services. According to reports, organizations have seen problems with sending and receiving email, while some users have encountered intermittent sign-in and access issues tied to Exchange Online services.
How This Affects Users
Users may experience:
- Delayed or undelivered emails.
- Intermittent authentication and sign-in failures.
- Difficulty accessing Outlook on the web or Exchange-connected applications.
- Disruptions to business communications that rely on Microsoft 365 email services.
What Organizations Should Do
While this issue is being addressed by Microsoft, businesses should:
- Monitor the Microsoft 365 Admin Center for updates related to EX1464935. – https://admin.cloud.microsoft/?#/servicehealth/:/alerts/EX1464935
- Advise users that email delivery may be delayed and to avoid repeatedly resending messages.
- Use alternate communication channels such as Microsoft Teams when necessary.
Security Perspective
At this time, Microsoft has identified the issue as a service availability problem rather than a cybersecurity incident. However, outages often create opportunities for phishing attempts that impersonate Microsoft support or service notifications. Organizations should remain vigilant and rely only on official Microsoft communications for status updates.
Update: September 1, 2026, 7:18 AM PDT
Microsoft has reported continued progress in recovering from the Exchange Online service disruption (EX1464935). According to the latest update, the issue has been traced to a problem within a core authentication configuration used by multiple Microsoft 365 services, resulting in impacts beyond Exchange Online.
Microsoft is actively deploying targeted remediation measures across remaining affected infrastructure and reports that service telemetry shows positive recovery trends
Users may be unable to connect to, or experience degraded functionality with Exchange Online
Issue ID: EX1464935
Affected services: Exchange Online
Status: Service degradation
Issue type: Incident
Start time: Aug 31, 2026, 8:08 AM PDT
More info
We’ve confirmed that the authentication component issue impacts other services beyond Exchange Online. For more information regarding other impact scenarios, please see: MO1465074.
We’ve opted to keep this post (EX1464935) open as Exchange Online remains the most predominantly impacted service.
Users may experience a variety of symptoms related to this event, including but not limited to:
– Delays, failures, or incomplete results when searching for content within Exchange Online mailboxes.
– Delays or failures when sending or receiving email messages.
– Authentication-related errors when accessing Exchange Online services.
– Difficulties accessing or performing actions within Exchange administration experiences.
– Intermittent failures affecting mailbox operations and message delivery work
– Delays or failures when sending or receiving email messages via Outlook for iOS and Android.
Scope of impact
Users attempting to perform any of the outlined impact scenarios may be affected by this event.
Root cause
An issue within a core authentication configuration used by multiple Microsoft 365 services is resulting in impact.
Current status
Sep 1, 2026, 9:00 AM PDT
Service telemetry continues to indicate recovery across previously impacted scenarios as remediation progresses through the remaining affected infrastructure. Core Exchange Online experiences, including mail flow and search functionality, have recovered. Our focus has shifted toward validating recovery across remaining Microsoft 365 services. We’re actively monitoring service health, assessing any residual pockets of impact, and confirming end-to-end functionality across affected workloads.