[Dovecot] Nested folders

hello,

I know this is a question that has probably been answered before but I have searched for the answer and am yet to find it.

I am running dovecot under fedora core 2 and cannot figure out where I set it so that users can create nested folders. At the moment they can only create one subfolder in most mail clients.

however if using squirrelmail they can create nested folders but the folder whicch hosts the subfolders cannot contain mail messages as well as folders.

Is this a setting in IMAP or with the mail clients.

Many Thanks,

melinda