ImapBack makes a complete copy of your emails, on any IMAP server, from Gmail to Google Apps, to your own custom IMAP server located anywhere in the world! These backups can be stored on another IMAP server, on our servers, or on your local hard drive. You can schedule any interval of backups (Daily, Hourly, Weekly, Monthly) as well as creating a backup on-demand.
On a related note, if you need an easy way to view and control IMAP access control, check out my IMAP ACL Manager application.