[Dovecot] Master account

Hi, Is there an administrator o master account in dovecot, which could be able too access all mailboxes? I need to periodically delete some emails (older than a number of days). I wanted to use imapfilter, a program that uses imap to access mailboxes to do that, but as the users can change their passwords, I can't do it. Is there a way to do that?

Thanks in advance, -- Diego.