Current best practice for automatically deleting email from mailbox?

My users do not use pop or imap to receive their mail, only forwarders. But they still use smtp to be able to have their email addresses appear in their emails' From: fields. What is the current best practice to delete emails from their mailboxes after, say, 30 days? I've seen cron jobs connected with a python script called archivemail, but am posting to see if there is anything better. Thanks!