To find out where an actual mailbox lives on disk, the mboxdir command is provided. It accepts a single email address as a parameter and outputs the calculated directory. Please note that it will always have output - the userbase is not contacted to determine if this mailbox is actually present in PowerMail.
This is actually a feature as it allows the operator to find orphaned mailboxes. It is useful to do the following:
~# cd $(mboxdir info@example.com) /var/messages/78/34/info@example.com# ls cur tmp /var/messages/78/34/info@example.com#