Can I turn off the Exchange cache mode message wich pops up at Outlook start when cached mode is disabled?

Yes, perform following steps:

  1. Close Outlook
  2. Open the file:
    "%AppData%\DocuWare\Connect to Outlook\CONNECTtoOutlookApplicationConfiguration.xml"
  3. Change the value for following parameter to "true":
  4. Save the changes

Now the message regarding Exchange cache mode is not displayed anymore. Please note that this doesnt mean that you don't need the Exchange mode anymore. This is still a requirement to use Connect to Outlook!