calendar - conflicting invitations

[G.Spellauge]

hello,

just downloaded and installed the kolab-software. at a first glance, it 
looks nice to me.

what's puzzeling me is the fact, that i could not find a way to 
configure a user/a resource in order to disallow calendar double booking 
- multiple bookings always seem to be accepted. could you please give me 
a hint where to find the appropriate docs?

thank  in advance, g.sp.