Currently Gmvault gives you the ability to save your emails on disk and restore them on any Gmail account with all the features. For example labels will be restored as identical. Many email backup tools are very generic and you will loose quite a lot of information when restoring your emails in a blend IMAP Server. Now all emails are stored in individual EML files with a unique filename. It is quite open and it should be pretty easy to create a Maildir structure. I will add that in the roadmap for v2.0. I am not convinced by mbox because it is a unique file with all the emails concatenated in it. I will see what to do with it.