November 12, 2026 — Microsoft is investigating a widespread Microsoft 365 service disruption that is affecting access to Outlook and Exchange Online mailboxes for users across multiple regions, according to the company’s service health page.
What Is Happening
Microsoft has confirmed it is looking into problems accessing Exchange Online mailboxes, tracked under incident ID EX1550543 in the Microsoft 365 admin center. In its status updates, the company said the issue “may affect Microsoft 365 service connectivity for users in any region,” with a later note pointing to problems across multiple connection methods in the Americas. Thousands of user reports have appeared on outage-tracking sites such as Downdetector.
Microsoft’s Response
Microsoft says it is working to mitigate the impact and has begun redistributing connection traffic across its broader worldwide infrastructure to help balance the load. At the time of writing, the company had not published a root cause, and the incident had not been marked as resolved.
What This Means for Your Business
If your team relies on Outlook or Exchange Online, you may see slow or failed sign-ins, emails that will not send or receive, or mailboxes that will not load in desktop, web and mobile apps. Messages sent to your organization are generally queued and delivered once service is restored, but delays are possible in the meantime.
What You Can Do Right Now
- Check the Microsoft 365 service status page or the Service health dashboard in your admin center for live updates on incident EX1550543.
- Avoid repeatedly resetting passwords or reinstalling Outlook; the problem is on Microsoft’s side and these steps will not help.
- Use a phone call, a messaging tool or another channel for urgent communication until email is stable.
- Let clients and staff know that replies may be delayed.
- Once service returns, confirm that outgoing messages stuck in your Outbox were sent.
Need Help?
Outages like this are a reminder of why a continuity plan matters, from backup communication channels to mail flow monitoring. If your business needs help assessing the impact or building a resilience plan for Microsoft 365, the System Support Canada team is here to help.
This is a developing story and details may change as Microsoft provides further updates. Sources: Microsoft 365 service health; KSAT; Outage.com.
