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 (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 ess-sp6-d ess-sp3-d ess-julia ess-r-d compile ess-tracebug format-spec ess-roxy hideshow ess-help ess-developer ess-r-args ess-s-l ess ess-inf comint ansi-color ring ess-mode ess-noweb-mode ess-utils ess-custom 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))