Microsoft Fixes Bug

Overview Microsoft has resolved a known issue that caused the Copilot Chat and Copilot buttons to disappear from Classic Outlook for Windows, affecting users with the Copilot Chat (Basic) license. The fix, rolled out on June 29, 2026, restores the missing interface elements and ensures seamless access to Copilot’s productivity features.

The Issue

Affected users reported that Copilot buttons were missing from multiple areas of Outlook:

• Ribbon toolbar missing Copilot icon — the top‑right button above the ribbon vanished.
• Left app bar or More Apps area missing Copilot — the sidebar icon was gone.
• Add Apps menu unresponsive — Copilot appeared as an available app but wouldn’t open.
• Ribbon customization grayed out — manual addition showed the command as unavailable.

Despite these UI issues, Copilot Chat remained accessible through Outlook on the web, the Microsoft 365 Copilot standalone app, and the web experience.

Microsoft’s Fix

The Outlook Team implemented a service change on June 29, restoring the missing buttons. Microsoft recommends:

• Restart Outlook to apply the update immediately.
• Update to the latest build via File > Office Account > Update Options > Update Now.
• Revert to previous Current Channel build if upgrading is not possible.
• Use new Outlook or OWA as temporary alternatives.

Related Outlook Issues

Microsoft is also investigating a crash issue linked to Kaspersky Antivirus and its Mail Checker module (mcou.dll). Affected users should:

• Check the Application log for Event 1000 entries with OUTLOOK.EXE and MCOU.DLL.
• Contact Kaspersky support if these faults appear.

This follows recent fixes for issues that blocked email sending via Outlook.com and caused instability when using the Microsoft Teams Meeting Add‑in.

Expert in the Cloud Insight

The Outlook Copilot button bug highlights the complexity of integrating AI features into legacy desktop clients. While web‑based Copilot experiences remain stable, desktop users should prioritize regular updates to avoid UI and compatibility issues.

For IT administrators, the lesson is clear: monitor service health notifications and apply updates promptly to maintain Copilot’s availability across Microsoft 365 apps.