Hello Timo,

if i use "hidden = no" at the private namespace, the complete namespace 
isn't viewable,
    
"complete" meaning what? Some do show? 
I don't see any folder in the private namespace. I see only the folder of public namespace.
I tried this configuration once more and the same happend.

>if i use "hidden = yes" i see the prefix "private" at   
>the foldernames in my emailclient. 
you haven't configured "private" prefix anywhere, so they're probably i
the mailbox narivate."... mes themselves..?
no. if i didn't configure the option "hidden" i saw all normal. I couldn't verify this effect this evening :-(

if use / as the seperator like dokumented at the wiki it doesn't work. 
    

Why? Probably a client problem.
  
Now it works... don't ask me why :-(

Well, Dovecot doesn't currently really support these kind of shared
mailboxes, but you might be able to kludge it:

With ACL plugin you can create dovecot-acls file to the maildirs that
you want to share to others. http://wiki.dovecot.org/ACL
  
I will see it. I hope this kind of ACLs work with virtual users. For my kind of LDAP stored ACLs i can use a python script to generate the files.

Mfg.
Stefan Klatt