[Dovecot] Dovecot read only for users

All,

I have hopefully a base question. How do you give users only read access to their inbox and folders? If I use chmod 600 they have full access. If I do a 400 they have read access but cannot access their inbox.
The config file is the out of the box config other than advertising IMAP and IMAPS.

Any help will be appreciated. Thanks.