Incident ID: EX1173828 | Status: Service Degradation | Date: October 18, 2025
Microsoft has confirmed a service degradation affecting Exchange Online users across multiple regions. The issue, tracked under EX1173828, is causing users to be unexpectedly signed out from Outlook on the web when accessing shared mailboxes.
What’s Happening
According to Microsoft’s advisory, the problem stems from authentication latency within Microsoft Entra ID, which is disrupting session continuity for shared mailbox access. The issue is not isolated to a specific tenant or region—any user accessing shared mailboxes via Outlook on the web may be affected.
Admins monitoring the Microsoft 365 Service Health Dashboard began seeing alerts late Thursday, with the next official update scheduled for Friday, October 17, 2025, at 10:30 PM UTC.
Real-World Impact
In live environments, this bug is more than a nuisance. Shared mailboxes are often used for:
- Support queues
- Finance and HR communications
- Project-based collaboration
When users are kicked out mid-session, it disrupts workflows and can lead to missed emails or duplicate responses. One admin in Bengaluru noted, “We had to temporarily redirect our support traffic to individual mailboxes just to keep things moving.”
What Admins Can Do
While Microsoft works on isolating the root cause, here are some interim steps admins can take:
- Switch to Outlook desktop clients or mobile apps, which appear less affected.
- Avoid shared mailbox access via browser until the issue is resolved.
- Monitor session logs for repeated sign-outs and notify affected users proactively.
- Use Microsoft 365 Admin Center to track updates under Exchange Online → EX1173828.
Broader Context
This incident follows a string of Microsoft 365 outages in October, many linked to Entra ID authentication delays and Azure Front Door routing issues. While Microsoft has not confirmed a direct connection, the pattern suggests deeper architectural stress in identity and routing layers.
This isn’t the first time shared mailboxes have tripped up Outlook Web Access, but the Entra ID angle adds a new wrinkle. As Microsoft continues to unify identity across services, even minor latency can ripple across critical workflows.
If you’re running hybrid environments or relying heavily on shared mailboxes for customer-facing roles, this is a reminder to build fallback channels and monitor session health more aggressively.
Have you faced similar sign-out issues this week? Did switching clients help? Drop your workaround or war story in the comments—we’re all navigating this together.
