dovecot --version 1.1.18 mbox format

We are trying to migrate from dovecot to another imap server and need some help migrating the user data to the new server. We have written a perl script to migrate the data but it seems that we need an "authenticated or Master user" in order for the script to access the user mail boxes without the users password. We are using PAM authentication, and root does not have access to the user's mail boxes. Any help would be appreciated. Chris