[horde] Can't understand the way Horde manages users

[Tô]

Hi list,

I'm about to make my Horde/Kolab server in production after quiet a year 
of tests.
Important thing : my preferences driver is Kolab
My configuration isn't absolutely perfect but...most of fundamentals are 
there.

One exception : I have no Horde users ! All of them are created via 
Kolab...and don't appear in Horde's users list.
Very difficult to set permissions, groups and other stuff in this case.

When I add a new user within Horde, its mailbox is created and appears 
in Horde's users list.
But I can't see users created with Kolab's web interface in Horde. And, 
of course, I can't create an existing Kolab's user with Horde's interface.

So I'm wondering if users created with Kolab should appear in Horde's 
users list ?
If not, how can I deal with it since I need Horde's users to set up 
permissions and groups ?

Just a point in the right way will be extremly appreciated.

Thanks in advance,

Christophe