This seemed simple to me at first, but our shell accounts and our email accounts do not seem related to each other on dreamhost.
All I want to do is have a script somewhere that does this:
daily: move all mail from inbox.tomorrow to inbox
weekly: move all mail from inbox.next_week to inbox
monthly: move all mail from inbox.next_month to inbox
The problem is that the shell account where you can edit the crontab is unrelated to the email account with the mail folders.