With Mail Backup X, your emails will always be safe.
It's not only an Apple Mail Archive PDF backup tool, you can actually back up all the messages from programs like as Thunderbird, Outlook, Entourage and Apple Mail.
With this program, you can also backup emails from Gmail and Yahoo or any web-based app that has IMAP services.
You can keep your files on your drive, or add them to flash drives and external HDDs. The program is able to detect all the messages in your mailboxes and you'll never lose your emails again.More details: Use This Apple Mail Archive PDF Backup Program And You Will Never Lose Your Emails Again