I`ve always wanted to have a copy of all my mails available locally so that in case am somewhere with connectivity issues i can still access my mail. There an application called GMAIL BACK UP. this is a standalone application that allows you to log into your gmail account and locallly back up all you mail. it save the backed up content in .eml format which allows other applications to access the content. the other thing i like about it is that it backs up your mails including the attachements and it has a small memory footprint compared to other clients such as thunderbird. for further information click HERE and if you`re interested in downloading the application click DOWNLOAD GMAIL BACKUP
check out this screenshot of Gmail Backup
check out this screenshot of Gmail Backup