When user creates an event and marks it as Private or Confidential, other users who have read access to the calendar can see the event. The way this is called (private, confidential) makes users around me (including me) suppose that the event will not be visible to others.

The issue has been raised here: https://kolab.org/hub/topic/76/handling-of-private-events/3

For reference:

FreeMinded: As far as I understand Kolab is using a two calendar concept to handle private events even though a flag private/confidential exists but does not affect visibility of the information to other users. In Outlook in contrary uses one calendar and hides the information from other users.

From a usability point of view the Outlook approach seems more natural and intuitive to me.

The information I find online seems to be quite old. See https://roundup.kolab.org/issue1041 (2006-2009), https://roundup.kolab.org/issue3613 (2009), http://lists.kolab.org/pipermail/devel/2006-January/004845.html (2006)

aseigo: We've talked about using Outlook elsewhere before on the forum here, so I won't repeat that bit, but respecting events marked as private is an interesting issue ... primarily this is because the calendar data is stored in folders and permissions are per-folder .. not per-file. So the filtering would always be client-side due to that, which renders the private (or other such "please filter this out") flags to not be very impactful. The solution would be to have server-side filtering of that content, though at that point one would want to index all the objects and filter that way .. with a proper index on that flag in hand, perhaps something that the Guam IMAP proxy/filter could do the work.