Microsoft has resolved a known bug that caused Copilot Chat and Copilot buttons to disappear in Classic Outlook for Windows users holding a Copilot Chat (Basic) license. The Outlook Team applied a service-side change on June 29, 2026, to address the problem.

What Was Affected

Users experiencing the issue reported several related symptoms:

  • The Copilot button missing from the top-right area above the ribbon.
  • The Copilot icon absent from the left app bar or the More Apps area.
  • Copilot appearing as an available app in Add Apps, but selecting Open producing no result.
  • Attempting to add Copilot through ribbon customization showing the command as unavailable or grayed out.

Microsoft confirmed that Copilot remained accessible through alternative entry points during the outage, including Outlook on the web, the Microsoft 365 Copilot standalone app, and the Copilot web experience.

Remediation Steps

Users who still cannot see the Copilot buttons after the service change are advised to restart Classic Outlook to pick up the fix immediately. Updating to the latest build is also recommended via File > Office Account > Update Options > Update Now.

For users unable to update, Microsoft suggests reverting to the previous Current Channel build (16.0.20026.20168) as a workaround, or switching to the new Outlook client or Outlook Web Access (OWA).

Separate Kaspersky Crash Issue Under Investigation

Microsoft is separately investigating unexpected Outlook crashes on systems running Kaspersky Antivirus software. The crashes are linked to the Kaspersky Mail Checker module (mcou.dll). Affected users running Outlook for Microsoft 365 can confirm whether this module is responsible by checking the Windows Application event log for Event ID 1000 entries listing OUTLOOK.EXE as the faulting application and MCOU.DLL as the faulting module. Microsoft is directing affected users to contact Kaspersky support for assistance while its own investigation continues.

These incidents follow a string of recent Classic Outlook reliability problems, including previously resolved issues that blocked email sending via Outlook.com and rendered the client unusable for users with the Microsoft Teams Meeting Add-in enabled.