I use notmuch-emacs as my MUA. When i go to send mail, it uses mml-mode to compose a message, just like this bug report. If i try to sign the mail using C-RET c p ( which is mml-secure-message-sign-encrypt), it inserts the mml signing tag like this (but without the space between the first anglebracket and the #): < #secure method=pgpmime mode=signencrypt> When it goes to encrypt upon sending, though, it chooses the encryption key(s) by doing a case-sensitive match on the recipient e-mail address. This match should be case-insensitive. note that gpg's attempt to match e-mail addresses specifically uses this form: gpg --list-keys '' and gpg itself is case-insensitive for this match. The domain part of an e-mail address clearly should be case-insensitive. And while technically the local-part of the e-mail address may not be case-insensitive, in practice on the modern SMTP network, e-mail address local parts are treated as case-insensitive, and mml-mode should follow this practice as well. enigmail recently fixed a bug with case-sensitive matching as well: https://sourceforge.net/p/enigmail/bugs/323/ Regards, --dkg In GNU Emacs 24.4.1 (x86_64-pc-linux-gnu, GTK+ Version 3.14.5) of 2014-12-09 on gaia, modified by Debian Windowing system distributor `The X.Org Foundation', version 11.0.11602901 System Description: Debian GNU/Linux 8.0 (jessie) Configured using: `configure --build x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/lib --localstatedir=/var/lib --infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes --enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.4/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.4/site-lisp:/usr/share/emacs/site-lisp --build x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/lib --localstatedir=/var/lib --infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes --enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.4/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.4/site-lisp:/usr/share/emacs/site-lisp --with-x=yes --with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2 -fstack-protector-strong -Wformat -Werror=format-security -Wall' CPPFLAGS=-D_FORTIFY_SOURCE=2 LDFLAGS=-Wl,-z,relro' Important settings: value of $LANG: en_US.UTF-8 locale-coding-system: utf-8-unix Major mode: Lisp Interaction Minor modes in effect: diff-auto-refine-mode: t savehist-mode: t display-time-mode: t shell-dirtrack-mode: t tooltip-mode: t electric-indent-mode: t mouse-wheel-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 line-number-mode: t transient-mark-mode: t Recent input: M-x r e p o r t - e m Recent messages: Loading /usr/share/emacs24/site-lisp/haskell-mode/haskell-mode-autoloads.el (source)...done Loading /etc/emacs/site-start.d/50haskell-mode.el (source)...done Loading /etc/emacs/site-start.d/50js2-mode.el (source)...done Loading /etc/emacs/site-start.d/50notmuch.el (source)...done Loading /etc/emacs/site-start.d/50ocaml-mode.el (source)...done Loading /etc/emacs/site-start.d/50php-elisp.el (source)...done Loading /etc/emacs/site-start.d/50python-docutils.el (source)...done Loading /etc/emacs/site-start.d/51debian-el.el (source)...done No desktop file. For information about GNU Emacs and the GNU system, type C-h C-a. Load-path shadows: /usr/share/emacs24/site-lisp/cmake-data/cmake-mode hides /usr/share/emacs/site-lisp/cmake-mode /usr/share/emacs/24.4/site-lisp/debian-startup hides /usr/share/emacs/site-lisp/debian-startup /usr/share/emacs24/site-lisp/dictionaries-common/flyspell hides /usr/share/emacs/24.4/lisp/textmodes/flyspell /usr/share/emacs/site-lisp/rst hides /usr/share/emacs/24.4/lisp/textmodes/rst /usr/share/emacs24/site-lisp/dictionaries-common/ispell hides /usr/share/emacs/24.4/lisp/textmodes/ispell Features: (shadow sort gnus-util mail-extr emacsbug notmuch hl-line notmuch-version notmuch-message notmuch-maildir-fcc notmuch-hello wid-edit notmuch-tree notmuch-parser notmuch-show notmuch-print notmuch-crypto notmuch-mua notmuch-address notmuch-wash diff-mode coolj notmuch-query goto-addr icalendar diary-lib diary-loaddefs cal-menu calendar cal-loaddefs notmuch-tag crm notmuch-lib cl gv message sendmail rfc822 mailabbrev mail-utils gmm-utils mailheader mm-view mml-smime smime password-cache dig mailcap mml mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 rfc2047 rfc2045 ietf-drums mm-util mail-prsvr savehist time desktop frameset debian-el debian-el-loaddefs haskell-mode-autoloads edmacro kmacro cl-loaddefs cl-lib ido ess-toolbar ess-mouse mouseme thingatpt 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 make-regexp ess-sp6-d ess-sp3-d ess-julia ess-r-d compile ess-tracebug format-spec ess-roxy advice hideshow ess-help ess-developer ess-r-args eldoc help-fns ess-s-l ess ess-inf comint ansi-color ring ess-mode ess-noweb-mode ess-utils ess-custom executable easymenu ess-compat ess-site emacs-goodies-el emacs-goodies-custom emacs-goodies-loaddefs easy-mmode dpkg-dev-el dpkg-dev-el-loaddefs bbdb-autoloads time-date tooltip electric uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image regexp-opt fringe tabulated-list newcomment lisp-mode prog-mode register page menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock syntax facemenu font-core frame cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean japanese hebrew greek romanian slovak czech european ethiopic indian cyrillic chinese case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer 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 make-network-process dbusbind gfilenotify dynamic-setting system-font-setting font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs) Memory information: ((conses 16 145009 11093) (symbols 48 26754 0) (miscs 40 55 141) (strings 32 34798 5223) (string-bytes 1 1119203) (vectors 16 17921) (vector-slots 8 466498 3885) (floats 8 121 60) (intervals 56 318 0) (buffers 960 12) (heap 1024 35134 1063))