MailStore Home enables you to backup all your e-mail messages from multiple applications into one persistent and safe archive. You can import your mail from Outlook, Windows Mail, Outlook Express, Thunderbird, Exchange, as well as POP/IMAP accounts and local files. You read your mail from within the interface, search fast through all your messages by keyword and advanced criteria, and even burn a Backup CD with the click of a button or export messages to .eml format. Messages are stored MIME-compatible, and can be recovered at any time without information loss.

http://www.mailstore.com/en/mailstore-home.aspx