Microsoft has fixed a known issue causing the Copilot Chat or Copilot buttons in Classic Outlook to disappear for Windows users with the Copilot Chat (Basic) license.
As the company explains in a recent support document, affected users may no longer see Copilot buttons on the side navigation and above the ribbon.
Those affected may also experience one or more of the following issues:
- The Copilot button is missing from the top-right area above the ribbon.
- The Copilot icon is missing from the left app bar or More Apps area in classic Outlook.
- In Add Apps, Copilot may appear as an available app, but selecting Open does nothing.
- Adding Copilot through ribbon customization may show the command as unavailable or grayed out.
- Copilot remains available from other entry points, such as Outlook on the web or the Microsoft 365 Copilot standalone app or web experience.
Microsoft says the Outlook Team has addressed this issue with a service change on June 29, 2026, and advised those who are still unable to see the Copilot buttons in Classic Outlook to restart their email client to get the change immediately.
Affected customers are also recommended to update to the latest build by selecting File > Office Account > Update Options > Update Now.
Those who can't upgrade their client to fix the bug can also work around the issue by reverting to the previous Current Channel build (16.0.20026.20168) or using the new Outlook or Outlook Web Access (OWA).
Microsoft is now also investigating a known issue that causes unexpected Outlook crashes on systems running Kaspersky Antivirus software, linked to the Kaspersky Mail Checker (mcou.dll).
Affected Outlook for Microsoft 365 users are advised to check the Application log for "Event 1000" events with the OUTLOOK.EXE faulting app name and MCOU.DLL faulting module name to confirm that this issue triggers the crashes.
"If you are experiencing this crash, please contact Kaspersky support," the Outlook Team said.
In recent months, Microsoft also resolved known issues that prevented some Classic Outlook users from sending emails via Outlook.com and rendered the client unusable for users who enabled the Microsoft Teams Meeting Add-in.
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