[Dovecot] Problem in sharing mailboxes across users

[Rampage]

Hello everyone,
I'm trying to configure dovecot to allow users to share their imap folders.
I've followed the wiki and i'm near to accomplish my tasks, when i set 
ACL properly on folders using imap commands the other user can see the 
folder as shared, but i can't subscribe to it or even access its content 
using any email client (like thunderbird) couse it looks like the path 
to the shared folder is not complete.

i mean when i go to "manage subscriptions" i can see the shared folder 
from the other users as "shared/user at domain/sharedfoldername" but since 
only "sharedfoldername" is present i cant subscribe to it.

am i missing somethimg? like do i need to setup a particular directory 
tree on the filesystem?

thnx in advice for your help.

Best regards.
Francesco.