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\\):’.