138: Why does Rmail think all my saved messages are one big message?

  A file created through the FCC: field in a message is in Unix mail
  format, not the format that Rmail uses (BABYL format).  Rmail will try to
  convert a Unix mail file into BABYL format on input, but sometimes it
  makes errors.  For guaranteed safety, you can make the saved-messages
  file be an inbox for your Rmail file by using the function
  set-rmail-inbox-list.