AOL Personal Filing Cabinet
The America Online (AOL) software stores email and web bookmarks (also known as "favorites") in a file known as the PFC (Personal Filing Cabinet) format. The format is different between Mac and PC versions apparently. The extension is either .pfc or nothing- see here for some details on the extension.
PFC-Viewer tool that can view and export emails from Personal Filing Cabinets. Source code available here: https://github.com/ernieyu/pfcviewer or here: http://home.roadrunner.com/~ernieyu/pfcviewer/pfcview-0.5-src.jar
http://web.archive.org/web/20050420101922/http://members.aol.com/fvongordon/pfc/documentation.htm This is the work that PFC Viewer was based on- there's some info about the format, and the program the person made, plus a text file of the file format details PFC-Details.zip download.