I use archivemail for regular deleting mails from my Junk folder:
archivemail --days=30 --delete $MAILDIR/.Junk
However, there is often mail in my Junk folder with a date in the future, often several years. Of course these mail are not covered by the "--days 30" flag and reside in my Junk folder for months nd years until I remove them manually.
I thus suggest to add another flag, that takes a date or a number of days as an argument so that also mails are selected whose dates are *newer* than the given date or more than the given number of days in the future.