CiviMail should have an optional auto-archiving feature

CiviMail should have a setting in the admin tool to auto-archive mailings after a specified time period. This should probably be triggered by a cron job. Otherwise they tend to accumulate in the Scheduled and Sent list because users don't realize they can archive them and/or don't take the time to do it. Then they complain that they can't find their mailings in the list.