141: How do I recover my mail files after Rmail munges their format?

  If you have just done rmail-input on a file and you don't want to save it
  in Rmail's format (called BABYL), just kill the buffer (with C-x k).

  If you typed M-x rmail and it read some messages out of your inbox and
  you want to put them in a Unix mail file, use C-o on each message.

  If you want to convert an existing file from BABYL format to Unix mail
  format, use the command M-x unrmail: it will prompt you for the input and
  output file names.