[Dovecot] Migration problems from Courier-Imap

Hi, I'm migrating from Courier-Imap to Dovecot-Imapd and I have some problems.. I don't want to change the IMAP folders, so I wish to have Dovecot's compatibility with Courier's IMAP folders. In the Dovecot configuration I configured this:

namespace private { separator = . prefix = INBOX. inbox = yes }

Dovecot correctly shows me the INBOX folder, but doesn't show me the subfolders anymore...

What can I do to solve this problem?

Thank you very much and goodbye. Mattia.