The message-bounce
command will, if the current buffer contains a bounced mail
message, pop up a message buffer stripped of the bounce
information. A bounced message is typically a mail
you've sent out that has been returned by some
mailer-daemon as undeliverable.
Headers
that match the message-ignored-bounced-headers
regexp will be removed before popping up the buffer. The default
is ‘^\\(Received\\|Return-Path\\|Delivered-To\\):’.