[Dovecot] Migrating mbox to maildir

Sorry to bother everyone but I was wondering if it is possible for Dovecot to handle mbox AND maildir at the same time?

Example:

I want to convert from UW Imap using mbox to Dovecot using maildir.

Do I need to convert ALL my users mbox mailboxes to maildir right away or can I convert them one at a time?

I'd like to use maildir with all my new users, but I'd like to be able to continue using mbox for my old users and slowly convert them as I get time.

Is this possible? I know Dovecot supports both formats, I just couldn't find anything in the install notes about using both at the same time.

Thank you,

mike