[Dovecot] How to specify /var/spool/mail/m/i/mike

I was wondering if somebody could tell me how I can tell dovecot (IMAP) to read users' mail boxes at /var/spool/mail/{1st char}/{2nd char}/username .

For example: Mailbox for user 'mike' would be located at /var/spool/mail/m/i/mike 'karen' would be at /var/spool/mail/k/a/karen etc...

Is this possible is version 1.1.6?

Please advise.

Thanks JB