bug#13329: 24.2 post patch for #9521; Rmail forward does not correctly handle MIME messages containing "From " lines

[Eli Zaretskii]

> From: Mark Lillibridge <mdl@alum.mit.edu>
> Cc: eliz@gnu.org, larsi@gnus.org, 13329@debbugs.gnu.org
> Date: Mon, 10 Oct 2022 14:04:58 -0700
> 
> >      I was using Emacs Rmail, but not the pure emacs 28.1 -q because I
> >  need to change settings to send email.  Let me see if I can try a purer
> >  reenactment.
> 
>     Ok, I sent myself a message with last line "From nothing" (pure text
> body); fetchmail produced the attached incoming_sample.gz file, which
> Rmail 'g' added to an empty Rmail file to produce the attached
> RMAIL.sample.gz.  I did this using as pure an Rmail set up as I can with
> emacs 28.1.  My sending/receiving goes through MIT email forwarding and
> uses Gmail as a receiving service.
> 
>    Both of these files have the proper mbox quoting, with a > before the
> >From in the body.  If I switch to emacs 28.1 -q and open that Rmail
> file, I see the extra > and pressing 'f' includes it in the forwarded
> message.  This shows both bugs (13328 and 13329).
> 
>    See if you can open RMAIL.sample and reproduce the bugs on your end.
> If so, something must differ between our email sending/receiving before
> rmail processes.  If you can't reproduce the bugs given the Rmail file,
> I'm very confused.

So, to summarize:

  . the problem happens only in emails that have MIME-Version: header
  . the problem happens only in emails that have just the body, no
    attachments
  . the problem happens because rmail-show-mime doesn't remove the ">"
    from ">From" when it shows the plan-text MIME content

Is that correct?