Microsoft 365 Outage: What Businesses Should Do Now

Microsoft is investigating connectivity problems affecting Exchange Online and other Microsoft 365 services on November 12. Users may be unable to open mailboxes or reach other services, and the experience can vary by tenant, location and application. If your organization is affected, coordinate a business response while Microsoft works on the service.

What Microsoft has confirmed

In the Microsoft 365 admin center, Microsoft lists EX1550543 for Exchange Online mailbox connectivity and MO1550821 for the broader service issue. Microsoft says potentially affected services include Exchange Online, Teams, SharePoint Online, Microsoft 365 Copilot, Defender XDR, Planner, To Do and several Purview capabilities. Inclusion on that list does not mean every customer or function is unavailable.

For Exchange, Microsoft identifies Outlook on the web, MAPI, Exchange ActiveSync and REST API among potentially impacted connection methods. Trying a browser or another client can help assess the impact, but it may encounter the same service issue.

In its 2:57 p.m. Central update, Microsoft said it had validated an alternative health-check method on a subset of infrastructure and was applying it more broadly. It was also preparing automated recovery for unresponsive servers and investigating configuration changes as possible contributors. Microsoft had not confirmed a root cause or declared the broader incident resolved at that update. Do not assume an attack, DNS failure or data loss without evidence.

First 15 minutes: establish the facts

1. Check the incident, not just the application. In the Microsoft 365 admin center, select Health > Service health and open EX1550543 and MO1550821. Note the update time, affected services and next update. If the admin center is unreachable, consult Microsoft’s public service status and Microsoft 365 Status.
2. Record your impact. Ask the help desk to capture when symptoms began, affected locations and business functions, error messages and whether web, desktop and mobile clients are affected. Avoid collecting passwords or sensitive message content.
3. Assign an incident lead. Name one person to monitor Microsoft’s updates, one to coordinate the help desk and one to communicate business decisions. Agree on the next update time even if the answer is still “investigating.”

Keep essential work moving safely

• Use an approved alternate channel. If email or Teams is unreliable, use the organization’s established phone tree, status page or approved secondary messaging system. Confirm how staff should reach customers and suppliers.
• Prioritize time-sensitive work. Identify urgent customer requests, payment approvals, order processing and scheduled meetings. Maintain an access-controlled list of work to reconcile when service returns.
• Avoid risky changes. A service incident is not a reason to disable MFA, change DNS, remove security policies, rebuild profiles or repeatedly recreate accounts. Troubleshoot a local issue separately if the symptoms or scope do not match Microsoft’s incident.
• Protect sensitive information. Use only approved tools and storage for temporary work. Avoid forwarding company email to personal accounts or circulating confidential files through unapproved channels.
• Monitor security coverage. Microsoft lists Defender XDR and Purview capabilities as potentially impacted. Ask security and compliance owners to review the affected functions and activate documented alternate monitoring or escalation procedures where needed; confirm gaps rather than assuming controls failed everywhere.

What to tell employees

Replace the bracketed time and name your actual approved channel. If a customer deadline may be missed, contact the relevant account owner through a working channel rather than promising a restoration time Microsoft has not provided.

After service returns

1. Verify critical workflows. Test mailbox access, a controlled send and receive, Teams messaging, access to essential SharePoint content and any affected integrations. Recovery may be uneven; sample different locations and users.
2. Reconcile work. Check queued or delayed messages and business transactions before resending or repeating an action. Avoid creating duplicate orders or approvals. Confirm time-sensitive communications reached their recipients.
3. Review security and compliance. Check relevant Defender and Purview service health, alerts and processing backlogs; investigate any coverage gaps under your normal incident process.
4. Capture lessons. Record the outage timeline, business impact, what worked and any gaps in alternate communications, monitoring and recovery. Review Microsoft’s post-incident report when available.

Where to follow updates

• Microsoft 365 admin center: Health > Service health — search for EX1550543 and MO1550821 (authorized admin sign-in required).
• Microsoft service health status and Microsoft 365 Status — public information when available.
• Microsoft Learn: How to check Microsoft 365 service health — dashboard navigation and notification guidance.

For longer-term preparation, see our Microsoft 365 outage preparation guide. Microsoft’s next updates and recovery status may differ from this time-stamped snapshot.