In certain situations the Outlook Client application sends an "Application is busy" message back to OE (visibile in 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 of the cases, the MS Teams Com Addin is causing this behaviour/issue



  • Open Outlook Client
  • Click Add-ins
  • Click on "Manage" (at the bottom) and select COM Add-ins  and click on GO
  • un-select the following Add-In


  • Restart Outlook Client