Backup procedures

Howdy,

I have a particular situation where I have about 5 users using a large account in IMAP, and I have the need to backup the account daily or weekly or so. I was thinking about to copy the whole directory, each email is a file, it could probably work, but the dovecot index files would be damaged/wrong.

Is there a tool that could perform a backup (ex: yesterday), and when I inserted that backup, it just insert the emails and folders that were deleted today?

Thanks in advanced, Jorge