** Rmail has a new command M-x unforward-rmail-message, which extracts
a forwarded message from the message that forwarded it. To use it, select a message which contains a forwarded message and then type the command. It inserts the forwarded message as a separate Rmail message immediately after the selected one.

This command also undoes the textual modifications that are standardly made, as part of forwarding, by Rmail and other mail reader programs.