Thank you for your fast answer.
As far I can see your answer is related to Outlook. Could you please tell me which version of Outlook the screenshot is from?
For Outlook-Users it appears to be working.
Actually I'm using Thunderbird. And in Thunderbird I was not able to find a calender related to my mailadress from grommunio.
But if I understand you properly every user registered in grommunio has a standard-calender. Right?
Could you please tell me at what place the connection-data for this standard user calender is visible in the administration-gui?

Best regards