Table of Contents
- Introduction
- Incident Overview — EX1464935
- Symptoms Users Are Experiencing
- Root Cause — Authentication Configuration Issue
- Broader Impact — Multiple Microsoft 365 Services Affected
- Microsoft's Response and Remediation
- What Microsoft 365 Administrators Should Do
- What Outlook Users Should Do
- What About Delayed Emails?
- Next Update — 6:00 AM ET, September 1, 2026
- Final Thoughts
Introduction
Microsoft is continuing to address a significant service disruption affecting Exchange Online, the cloud email platform that powers Microsoft Outlook and Microsoft 365 email services worldwide.
The incident, identified as EX1464935, is causing users globally to experience difficulties connecting to Exchange Online, sending and receiving email, searching mailboxes, and performing certain Exchange administration and mailbox operations.
Microsoft has confirmed that the issue is related to a core authentication configuration used by multiple Microsoft 365 services.
Incident Overview — EX1464935
Microsoft's investigation has identified that the outage stems from a problem within a core authentication configuration used by multiple internal services within the Exchange Online infrastructure.
Because authentication is a fundamental component of Microsoft's cloud platform, an issue with this configuration can affect more than simply signing in. Exchange Online requests, mailbox operations, message delivery, and other service functions can also be impacted.
Incident Details:
- Incident ID: EX1464935
- Primary Service: Exchange Online
- Related Incident: MO1465074 (broader Microsoft 365 impact)
- Issue: Authentication configuration problem
- Impact: Email, mailbox access, search, authentication, and administration
- Status: Remediation in progress
- Latest Update: September 1, 2026
Exchange Online remains the most predominantly impacted service under this incident.
Symptoms Users Are Experiencing
Users may experience different symptoms depending on their mailbox and the affected infrastructure. Microsoft has identified several possible symptoms:
- Delays or failures when sending email
- Delays or failures when receiving email
- Authentication-related errors when accessing Exchange Online
- Problems connecting to Exchange Online
- Delays, failures, or incomplete results when searching mailboxes
- Difficulties accessing or performing actions in Exchange administration experiences
- Intermittent mailbox operation failures
- Delays or failures affecting message delivery workflows
If multiple users in your organization are experiencing similar Outlook problems simultaneously, the issue is likely related to Microsoft's service rather than individual computers.
Root Cause — Authentication Configuration Issue
Microsoft's investigation has identified an issue within a core authentication configuration used by multiple internal services within the Exchange Online infrastructure.
What does this mean?
- Authentication is a fundamental component of Microsoft's cloud platform
- An issue with authentication configuration can affect multiple service functions
- This is not limited to sign-in — it can affect email delivery, mailbox access, search, and administration
Microsoft has been analyzing service telemetry and diagnostic information while testing and deploying remediation measures.
Broader Impact — Multiple Microsoft 365 Services Affected
Although Exchange Online is the most significantly impacted service under EX1464935, Microsoft has also confirmed that the underlying authentication component issue can affect other Microsoft 365 services.
A separate incident, MO1465074, is being used to track the broader Microsoft 365 impact.
Reportedly affected Microsoft 365 workloads include:
- Exchange Online — most impacted
- Microsoft Outlook — desktop, web, and mobile
- Microsoft Teams — may experience connectivity issues
- SharePoint Online — may experience access problems
- OneDrive for Business — may experience sync issues
- Microsoft Purview — compliance features may be affected
- Microsoft Defender XDR — security features may be impacted
Organizations experiencing multiple Microsoft 365 problems should not automatically assume the issue is related to a local computer, Outlook installation, network connection, or individual user account.
Microsoft's Response and Remediation
Microsoft says engineers are continuing to reapply the targeted authentication component fix to the remaining affected infrastructure where necessary.
Current status:
- Service telemetry remains positive
- Overall service availability is improving
- Microsoft is monitoring the environment closely while remediation progresses
- Earlier updates indicated improvements in mailbox connectivity
Microsoft reports that service telemetry remains positive and overall service availability is improving as remediation continues.
What Microsoft 365 Administrators Should Do
If multiple users are experiencing similar Outlook or Exchange Online problems simultaneously, administrators should first determine whether Microsoft's service incident is responsible before making major configuration changes.
What NOT to do:
- Don't recreate Outlook profiles — this won't fix a service-side issue
- Don't reset user passwords without evidence of an account problem
- Don't change DNS records — the issue is with Microsoft's infrastructure
- Don't reconfigure Exchange connectors unnecessarily
- Don't remove and reinstall Outlook — this is a service issue, not a local one
- Don't change Microsoft 365 authentication policies unnecessarily
What TO do:
- Monitor Microsoft's Service Health dashboard for official updates
- Collect user reports to track the scope of the impact
- Compare symptoms across affected accounts
- Communicate with users about the ongoing issue
- Avoid unnecessary configuration changes that could complicate recovery
Making unnecessary changes during a Microsoft-side outage can create additional problems and make troubleshooting more difficult once the service begins recovering.
What Outlook Users Should Do
For most users, the best approach is to avoid making unnecessary changes to their Outlook configuration while Microsoft works on the service-side issue.
Steps for Outlook users:
- Check with your IT department or Microsoft 365 administrator before making changes
- Compare symptoms with colleagues — if others have the same issues, it's likely a service problem
- Avoid repeated login attempts — this may not help and can add load to affected systems
- Use alternative communication methods for urgent messages
- Monitor your IT team's updates for information on service recovery
If Outlook is showing authentication errors, repeatedly disconnecting, or failing to send and receive messages, users should first check with their IT department or Microsoft 365 administrator.
What About Delayed Emails?
Organizations experiencing delayed mail delivery should not immediately assume that messages have been permanently lost.
Important points about email delays:
- During a cloud service disruption, messages may be delayed while Microsoft restores affected infrastructure
- Messages are not necessarily permanently lost — they may be queued for delivery
- Once Exchange Online stabilizes, administrators can use message tracing to investigate delivery issues
- For business-critical communications, organizations should maintain alternative communication methods
During a cloud service disruption, messages may be queued and delivered once Microsoft restores affected infrastructure and mail-flow functionality.
Next Update — 6:00 AM ET, September 1, 2026
Microsoft's next scheduled status update is expected at:
Tuesday, September 1, 2026 at 6:00 AM ET
The original Microsoft Service Health timestamp is 3:00 PM GMT+5, which converts to 6:00 AM Eastern Time (ET) on September 1, 2026.
Important: The 6:00 AM ET time represents Microsoft's next scheduled status update, not a guaranteed resolution time. Microsoft may provide additional information regarding remediation, service availability, or the estimated time to full recovery.
Final Thoughts
The ongoing Exchange Online incident highlights how a problem within a shared authentication component can have a much broader impact across Microsoft's cloud ecosystem.
For Outlook users, the symptoms may appear to be an application problem — such as Outlook failing to connect, emails becoming stuck, or mailbox searches returning incomplete results. However, Microsoft's investigation indicates that the underlying problem is within the Microsoft 365 service infrastructure.
Key takeaways:
- Exchange Online outage (EX1464935) — authentication configuration issue
- Multiple Microsoft 365 services are potentially affected
- Remediation is in progress — Microsoft is applying targeted fixes
- Service availability is improving — telemetry shows positive signs
- Avoid unnecessary changes — don't make configuration changes during the outage
- Monitor Service Health — check Microsoft's official dashboard for updates
- Next update — expected at 6:00 AM ET on September 1, 2026
If your business is experiencing significant disruption due to the Outlook and Exchange Online outage and needs assistance, contact SystemLogicIT for expert guidance and IT support.