Microsoft investigates new Exchange Online outage as classic Outlook users hit with mailbox failures

Earlier last week, Microsoft began investigating an issue where Copilot for Microsoft 365 users were unable to trigger file-related actions, including opening or editing documents. That problem affected tenant-wide workflows and forced admins to seek workarounds while Microsoft worked on a fix.

These incidents surfaced shortly after multiple Azure outages reported across regions, along with brief Microsoft 365 outages that impacted authentication and Teams connectivity. For organizations heavily dependent on cloud-based workflows, the string of issues has raised fresh concerns about stability across Microsoft’s productivity stack.

Now, Microsoft is responding to a new outage affecting classic Outlook desktop users. The company acknowledged the problem under incident EX1189820, as reported by Bleeping Computer. According to Microsoft, customers are unable to connect to their Exchange Online mailboxes through the classic Outlook experience.

Users are reportedly also facing login failures and server connection errors. In a status update, Microsoft said, “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 outage appears to be affecting customers in the Asia Pacific and North America regions. Microsoft has not yet disclosed how many organizations are affected, but the incident carries the “significant impact” tag in the admin center, hinting at a bigger issue.

As a temporary workaround, the company recommends switching to Outlook on the Web, which remains unaffected. Alongside the connectivity failures, a separate outage, EX1189768, is causing issues for users relying on search within classic Outlook. This has prevented some users from retrieving results when using the search bar.

“Impact is specific to some users attempting to search in the classic Outlook desktop client. We’re analyzing service-side logs to identify the root cause and develop a mitigation plan,” Microsoft said.