First of all, there is a WP7 forum on this site. You are NOT on it.The tools and techniques published here will not work on your device (and vice versa). Additionally, many of the people here either never used WP7 or stopped using it long ago when WP8 came out.
With that said, there's no easy way that I know of (well, "stop using that antique Piece Of <REDACTED> protocol POP3; it's quite possibly older than you are" but I suppose that doesn't solve your current problem). The only thing that comes to mind is to use a homebrew app that access MAPI (the Mail API) and extracts the messages in that folder, then transfers them to your PC somehow (any number of ways are possible there, really; the trick is just getting the messages). I don't know if anybody has tried coding an app that accesses WP7 MAPI yet.