Microsoft Investigates Missing Copilot Buttons in Classic Outlook

Microsoft is investigating a technical issue that causes Copilot and Copilot Chat buttons to disappear within the Classic Outlook for Windows client.

The bug specifically affects users holding a Copilot Chat (Basic) licence or a paid Microsoft 365 Copilot (Premium) account. Affected individuals may find the Copilot icon missing from the left app bar, the top-right area above the ribbon, or within the “More Apps” section. In some instances, the Copilot app may appear available in “Add Apps,” but selecting “Open” results in no action.

Technical cause and affected builds

Microsoft confirmed that the issue typically occurs after upgrading Classic Outlook for Windows to build 20026.20182 or higher. Technical analysis indicates that in affected environments, Outlook is unable to locate the MAPI property PR_PROFILE_USER_SMTP_EMAIL_ADDRESS_W within the null profile section.

Because the component cannot locate this property, the Outlook Copilot element fails to persist in the necessary settings, which prevents the entry point from appearing in the navigation pane.

Available workarounds

While a permanent fix is under investigation, Microsoft has provided a temporary workaround to restore button visibility. Users can attempt to resolve the issue by enabling the “Show Apps in Outlook” option:

• Select the File tab.
• Choose Options.
• Navigate to the Advanced section.
• Under “Outlook panes,” check the box for Show Apps in Outlook.

Affected users can also access Copilot features through other entry points, such as Outlook on the web, the Microsoft 365 Copilot standalone app, or by switching to the “New Outlook” email client, which remains unaffected by this bug.

Kaspersky Antivirus compatibility issues

In a separate stability issue, Microsoft confirmed a bug causing unexpected Outlook crashes on systems running Kaspersky Antivirus software. These crashes trigger “Event 1000” entries in the application log and have been linked to the Kaspersky Mail Checker (mcou.dll).

Microsoft has advised customers experiencing these crashes to contact Kaspersky support while the Outlook team continues to investigate the compatibility conflict.