The format is proprietary (*.dbx files, but having nothing to do with Autesk's format by the same name), but I recall seeing a couple utilities years ago that would allow you to backup, save to other formats, etc. so somewhere the details of the format have to be published if you know the right handshake. Google it; see what ya find. Report back. :)
PS -- One thing I've done in the passed (if this is an archival issue of your own data) is simply copy the contents of an Outlook Express folder to a folder (directory) OUTSIDE of Outlook express, using dumb old drag and drop (undocumented I think). I then wrote a quick program to scan thru the resulting text files, pulling data that I wanted. My program ripped thru the data fast; the copying to a folder exercise was VERY SLOW; you'll think your PC died. It hasn't.
Over and out.