Microsoft is working to resolve an Exchange Online outage that is blocking classic Outlook for Windows from connecting to cloud mailboxes, leaving many users dependent on the web version of Outlook instead.
The company flagged the connectivity incident under ID EX1189820 at 09:57AM UTC on November 25th. The impact currently hits users in the Asia Pacific and North America regions who use the classic Outlook desktop experience to reach Exchange Online mailboxes, while Outlook on the web remains available as a fallback.
Scope of the Exchange Online outage
Microsoft’s service health message describes a straightforward but disruptive symptom: classic Outlook clients can’t connect to Exchange Online, triggering connection and login failures. User reports also show spikes in problems on outage tracking platforms as clients repeatedly attempt to reach servers.
| Incident ID | Issue | Affected client | Regions | Status |
|---|---|---|---|---|
| EX1189820 | Mailbox connectivity failures | Classic Outlook for Windows | Asia Pacific, North America | Investigating |
| EX1189768 | Search not working | Classic Outlook for Windows | Some users (unspecified) | Investigating |
In a notice to administrators, Microsoft says:
“Users may be unable to connect to their Exchange Online mailbox in the classic Outlook experience. We're actively investigating the root cause of the connectivity failures.”
The company also notes that the incident is tagged as an “incident” in the admin center, a classification typically reserved for problems with significant user impact across multiple tenants.
Classic Outlook search problems in a separate incident
Alongside the connectivity failures, Microsoft is also tracking a second issue affecting search inside the classic Outlook desktop client. That problem is logged as incident EX1189768 and was acknowledged at 05:05AM UTC on November 25th.
The impact is narrower but still noticeable: some users cannot retrieve expected results when searching in classic Outlook. Microsoft says engineers are reviewing service-side logs and working on a mitigation plan for the search failures.
Classic Outlook has a long list of known bugs and regressions documented on Microsoft’s support pages for recent issues in the client, including crashes, sign-in problems, and search anomalies in various monthly updates. The current search and connectivity incidents add to that history, but they sit at the service layer, not just the desktop app.
Workarounds and what users can do now
With no fix deployed yet for EX1189820 or EX1189768, Microsoft is steering affected users to Outlook on the web as the primary workaround. That keeps access to mail and calendar while the desktop client continues to fail against Exchange Online.
- Use Outlook on the web (OWA) to read and send email while desktop connectivity is broken.
- Use OWA search if classic Outlook’s search bar is returning incomplete or no results.
For many organizations, that means a temporary shift in workflows, especially for employees who rely on classic Outlook features or plug-ins that are not mirrored on the web. IT teams will need to communicate alternatives clearly and prepare for a bump in support requests while the outage is active.
Recent reliability issues around Microsoft 365 services
The new Exchange incidents follow a run of other cloud disruptions across Microsoft’s stack this fall. In late October, a DNS issue impacted Azure and Microsoft 365, blocking logins to corporate networks and cloud services. Earlier in October, a separate problem with Microsoft Entra multi-factor authentication broke single sign-on to Teams, Exchange Online, and the Microsoft 365 admin center. A day later, an Azure Front Door content delivery network fault took down Microsoft 365 services for customers across Europe, Africa, and the Middle East.
Classic Outlook itself has also had a rough year. Microsoft has documented multiple critical bugs in the client: everything from sign-in errors and startup crashes to a confirmed glitch that throws the “Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The attempt to log on to Microsoft Exchange has failed.” error and prevents the app from opening at all. In one recent case, that crash pattern was tied to Exchange Online throttling limits on busy mailboxes.
As of November 25th, Microsoft has not published a root cause or recovery timeline for EX1189820 or EX1189768. Admins are being told to monitor the Microsoft 365 admin center for updates while users lean on Outlook on the web and other clients to keep their inboxes moving.
