If you actually want to preserve those increments (as opposed to just keeping an rsync mirror up-to-date), I like rdiff-backup. It handles maildirs well because of the one-message-per-file design. Second that. It's great tool that keeps an actual sync (rsync-based) of the data-directory and the metadata (delta) in a seperate directory to restore data from any date.
Alternatively, you might want to take a look at bacula, which was faster in most cases (development seems to have stalled, but there is a fork I have not had time to take a look at: bareos). However, I liked the rdiff-backup way because I can restore files via scp or rsync (most of my requests were like "please restore from yesterday") or if I want to restore data from a certain date I can use rdiff-backup from command line (bacula is much more complex, and you need the admin tool to restore files - rdiff-backup works from command line locally or via ssh/keyauth)
hth, Robert