In certain situations, the Outlook Client application sends an "Application is busy" message back to OE (visible in the OE Log).

ERROR : OutlookHelper: System.Runtime.InteropServices.COMException (0x80004005): See inner exception(s) for details. ---> System.Runtime.InteropServices.COMException (0x8001010A): The message filter indicated that the application is busy. (Exception from HRESULT: 0x8001010A (RPC_E_SERVERCALL_RETRYLATER))

This error can occur if other third party tools are using/accessing the COM of the Outlook Client. In most cases, the MS Teams Com add-in is causing this behaviour/issue.


  • Open the Outlook client
  • Click on Add-ins
  • Click on Manage at the bottom, select COM Add-ins, and click on GO
  • Unselect the following add-in

  • Restart the Outlook client