Converting individual messages to mbox format

I have a directory (actually, a few hundred directories....) containing a bunch of files. Each file contains a single e-mail message, in RFC822 format. Can anyone point me to a utility to gather up all those files, and convert them to a single "mbox" format file, suitable for feeding into Hypermail?

I do have to be able to preserve the message dates, so any solution must get the message date from the RFC822 "Date:" header, and put it into the mbox "From_" line.

Thanks,
--Pat. Received on Thu 28 Oct 1999 07:11:11 PM GMT