bug#21733: 25.0.50; Umlaut in address makes smtpmail-via-smtp fail

[Stephen Berman]

I tried to send an email with Gnus to an address containing an umlaut
('ä') in the domain name, and it failed with the error "Sending failed:
501 Syntax error in parameters or arguments".  When I tried sending the
same email to the same address using the GMX webmail interface, it
succeeded.  A copy of the sent email showed an address containing only
ascii characters instead of the address with the umlaut, so I assume the
latter is aliased to the former and GMX automatically found this.  It
would be nice if smtpmail.el could do the same thing instead of erroring
out.  I can reproduce the same error using the fake address
<stephen.berman@gmx.nät> (backtrace attached).

In GNU Emacs 25.0.50.3 (x86_64-suse-linux-gnu, GTK+ Version 3.14.15)
 of 2015-10-16
Repository revision: b0d190fbe2cd4a092fa186b3d674ec89ff000776
Windowing system distributor 'The X.Org Foundation', version 11.0.11601000
System Description:     openSUSE 13.2 (Harlequin) (x86_64)

Configured using:
 'configure 'CFLAGS=-Og -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GCONF GSETTINGS NOTIFY
GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Message

Minor modes in effect:
  diff-auto-refine-mode: t
  gnus-message-citation-mode: t
  mml-mode: t
  show-paren-mode: t
  recentf-mode: t
  shell-dirtrack-mode: t
  display-time-mode: t
  tooltip-mode: t
  global-eldoc-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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  temp-buffer-resize-mode: t
  column-number-mode: t
  line-number-mode: t
  auto-fill-function: message-do-auto-fill
  abbrev-mode: t

Recent messages:
Back to top level
Mark set
Address ‘stephen.berman@gmx.nät’ (stephen.berman@ =?utf-8?Q?gmx=2En=C3=A4t?=) 
might be bogus.  Continue? (y or n) y
Sending...
Mark set [2 times]
Sending via mail...
Entering debugger...
Auto-saving...done
Making completion list...
Scanning for dabbrevs...done

Load-path shadows:
None found.

Features:
(shadow emacsbug mm-archive gnus-dup misearch multi-isearch find-dired
grep eieio-opt speedbar sb-image ezimage dframe edebug vc vc-dispatcher
vc-git diff-mode find-func debug mailalias smtpmail sendmail jka-compr
gnus-dired dabbrev nnir qp sort smiley gnus-cite mail-extr gnus-async
gnus-bcklg gnus-ml disp-table gnus-topic cursor-sensor nndraft nnmh
nnfolder gnutls network-stream nsm starttls gnus-agent gnus-srvr
gnus-score score-mode nnvirtual gnus-msg gnus-art mm-uu mml2015 mm-view
mml-smime smime dig mailcap nntp gnus-cache gnus-sum gnus-group
gnus-undo gnus-start gnus-cloud nnimap nnmail mail-source tls utf7 netrc
nnoo parse-time gnus-spec gnus-int gnus-range message dired-x dired
rfc822 mml mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231
rfc2047 rfc2045 ietf-drums mailabbrev gmm-utils mailheader gnus-win gnus
gnus-ems nnheader mail-utils edmacro kmacro view cal-china lunar solar
cal-dst cal-bahai cal-islam cal-hebrew holidays hol-loaddefs face-remap
appt tramp-gvfs zeroconf url-util url-parse url-vars dbus xml
tramp-cache tramp-sh tramp tramp-compat auth-source cl-seq eieio
eieio-core cl-macs gnus-util mm-util help-fns mail-prsvr password-cache
tramp-loaddefs trampver srb-light-theme paren recentf tree-widget
wid-edit cus-start cus-load srb-cal+diary+appt todo-mode diary-lib
diary-loaddefs cal-menu calendar cal-loaddefs ido seq byte-opt gv
bytecomp byte-compile cconv cl-extra help-mode ess-toolbar ess-mouse
mouseme browse-url ess-menu ess-swv ess-noweb ess-noweb-font-lock-mode
ess-bugs-l essd-els ess-sas-d ess-sas-l ess-sas-a shell pcomplete
ess-sta-d ess-sta-l cc-vars cc-defs cl-loaddefs cl-lib make-regexp
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executable ess-compat ess-site advice preview-latex tex-site auto-loads
w3m-load bbdb-loaddefs srb-recentf srb-mode-line time noutline outline
flotte-karotte srb-misc thingatpt pcase easy-mmode finder-inf package
easymenu epg-config time-date mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list newcomment
elisp-mode lisp-mode prog-mode register page menu-bar rfn-eshadow timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
frame 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 charscript
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer
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 dbusbind inotify
dynamic-setting system-font-setting font-render-setting move-toolbar gtk
x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 354322 68420)
 (symbols 48 53391 23)
 (miscs 40 364 966)
 (strings 32 97674 12934)
 (string-bytes 1 3264178)
 (vectors 16 40955)
 (vector-slots 8 1499368 196903)
 (floats 8 1015 386)
 (intervals 56 4237 595)
 (buffers 976 52)
 (heap 1024 93673 37196))

txtZ4DB60QypF.txt
Description: backtrace