Note 1: I assume similar code is needed in imap.el (RFC 6855), but I do
not have such a server, so I am not able to test a corresponding change.

Note 2: Using UTF-8 in the "Subject:" header does not work.  While the
subject is shown correctly in the summary, I get the usual bad display
in the mail itself.  But that should be a separate bug report, I think.

----

In GNU Emacs 28.2.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.24, cairo version 1.16.0)
 of 2022-11-22 built on zenobia
Repository revision: 0636e1066bbafcd8219d9a8e09301c77f875d78b
Repository branch: emacs-28
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Debian GNU/Linux 11 (bullseye)

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS
X11 XDBE XIM XPM GTK3 ZLIB

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

Major mode: Group

Minor modes in effect:
  global-git-commit-mode: t
  shell-dirtrack-mode: t
  gnus-topic-mode: t
  gnus-undo-mode: t
  desktop-save-mode: t
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  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
~/Projects/ttf-mode/arc-mode-compat hides ~/emacs/arc-mode-compat
/home/benny/.emacs.d/elpa/transient-20230315.1520/transient hides /usr/local/share/emacs/28.2.50/lisp/transient
/home/benny/.emacs.d/elpa/soap-client-3.2.1/soap-client hides /usr/local/share/emacs/28.2.50/lisp/net/soap-client
/home/benny/.emacs.d/elpa/soap-client-3.2.1/soap-inspect hides /usr/local/share/emacs/28.2.50/lisp/net/soap-inspect

Features:
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tramp-gvfs tramp-cache zeroconf tramp tramp-loaddefs trampver
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ol-docview doc-view image-mode exif ol-bibtex ol-bbdb ol-w3m ol-doi
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org-table oc-basic bibtex ol org-keys oc org-compat org-macs
org-loaddefs compile gnus-kill cl-print debug backtrace eieio-opt
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with-editor shell pcomplete magit-mode transient magit-git magit-base
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xt-mouse cal-china lunar solar cal-dst cal-bahai cal-islam cal-hebrew
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bytecomp byte-compile cconv cl-loaddefs cl-lib iso-transl tooltip eldoc
paren electric uniquify ediff-hook vc-hooks lisp-float-type elisp-mode
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 lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax 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 emoji-zwj charscript charprop case-table
epa-hook jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice
button loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
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 (strings 32 214519 18167)
 (string-bytes 1 8662819)
 (vectors 16 90518)
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 (intervals 56 14138 2200)
 (buffers 992 55))