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. Affected users may no longer see Copilot buttons on the side navigation and above the ribbon, and may experience issues such as the Copilot button missing from the top-right area above the ribbon, the Copilot icon missing from the left app bar or More Apps area, or Copilot appearing as an available app in Add Apps but selecting Open doing nothing. Microsoft says the Outlook Team addressed this issue with a service change on June 29, 2026, and advised those still unable to see the buttons to restart their email client or update to the latest build. Affected customers 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. Microsoft is now also investigating a known issue causing 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, and to contact Kaspersky support if experiencing the crash.