Windows 7 Tip: 
MailStore Home is a new Utility which enables you to backup all your email 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 can 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.
Features:
Keep Your E-Mail in One Safe Place Save Disk Space Lightning-Fast Search One-Click Backup Benefit From Your E-mail
Does it work with GMail? I have used about 240+MB space on my GMail account… It’ll will take a lot of time to backup, right?