bug#41975: 27.0.91; rmail and mbox does not render as gnus does

[rrandresf]

Hi. There.

I was trying to export  an email from gmail. and watching it inside
emacs.

gmail exports as eml. and there is a ruby utility eml2mbox, which I have
used for converting to mbox the eml file.

On emacs. I was trying to see which builtin mail client is simple for
opening mbox. For using less keystrokes rmail beat gnus. But rmail does
not render the email as gnus does. See the image below:

--8<---------------cut here---------------start------------->8---
http://0x0.st/i4BO.png
--8<---------------cut here---------------end--------------->8---

Also. I have tried this with emacs -Q

--8<---------------cut here---------------start------------->8---
M-x gnus
G f
path
--8<---------------cut here---------------end--------------->8---

--8<---------------cut here---------------start------------->8---
C-u M-x rmail
path
--8<---------------cut here---------------end--------------->8---

AR
ps:just in case. I am attaching the mbox file.

bug#41745 28.0.50; problem with json file and which-function on pretest an master.eml.mbox
Description: test_mbox

In GNU Emacs 27.0.91 (build 1, armv7l-unknown-linux-gnueabihf, X toolkit, Xaw3d 
scroll bars)
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Arch Linux ARM

Recent messages:
Reading active file from news via nntp...
Opening nntp server on news...
Server nntp+news previously determined to be down; not retrying
Opening nntp server on news...failed: >>> (error news/nntp Name or service not 
known)
Reading active file via nndraft...done
Checking new news...done
No news is good news
Warning: Opening nntp server on news...failed: >>> (error news/nntp Name or 
service not known); Server nntp+news previously determined to be down; not 
retrying; Opening nntp server on news...failed: >>> (error news/nntp Name or 
service not known); Server nntp+news previously determined to be down; not 
retrying
Opening nndoc server on /home/olla/downloads/bug#41745 28.0.50; problem with 
json file and which-function on pretest an master.eml.mbox...done
Counting messages...done

Configured using:
 'configure '--program-transform-name=s/^ctags$/ctags.emacs/'
 --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/usr/share --with-x-toolkit=lucid
 --mandir=/usr/share/man --pdfdir=/usr/share/doc/emacs --with-modules
 --with-xft --without-gconf --without-gsettings --with-imagemagick
 --without-xwidgets --without-pop --with-gameuser=:games
 --disable-build-details 'CFLAGS=-march=armv7-a -mfloat-abi=hard
 -mfpu=vfpv3-d16 -O2 -pipe -fstack-protector-strong -fno-plt'
 CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'

Configured features:
XAW3D XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GLIB NOTIFY
INOTIFY ACL GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS LUCID X11 XDBE XIM MODULES THREADS LIBSYSTEMD JSON
PDUMPER LCMS2 GMP

Important settings:
  value of $LC_COLLATE: C
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: RMAIL

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow emacsbug sendmail rmailmm cl-extra help-mode sort smiley
ansi-color gnus-cite mail-extr qp gnus-async gnus-bcklg gnus-ml
disp-table cursor-sensor nndoc nndraft nnmh network-stream nsm
gnus-agent gnus-srvr gnus-score score-mode nnvirtual gnus-msg gnus-art
mm-uu mml2015 mm-view mml-smime smime dig nntp gnus-cache gnus-sum url
url-proxy url-privacy url-expand url-methods url-history mailcap shr
url-cookie url-domsuf url-util url-parse auth-source cl-seq eieio
eieio-core cl-macs eieio-loaddefs json map url-vars svg xml dom
browse-url gnus-group gnus-undo gnus-start gnus-cloud nnimap nnmail
mail-source utf7 netrc nnoo parse-time iso8601 gnus-spec gnus-int
gnus-range message rmc puny dired dired-loaddefs format-spec rfc822 mml
easymenu mml-sec password-cache epa derived epg epg-config mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
gnus-win gnus nnheader gnus-util text-property-search time-date subr-x
seq byte-opt gv bytecomp byte-compile cconv wid-edit cl-loaddefs cl-lib
rmail rmail-loaddefs rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode elisp-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame minibuffer cl-generic
cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting font-render-setting x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 8 132994 14624)
 (symbols 24 15381 1)
 (strings 16 44638 3746)
 (string-bytes 1 1557205)
 (vectors 8 22557)
 (vector-slots 4 332467 19682)
 (floats 8 223 47)
 (intervals 28 479 0)
 (buffers 576 24))