The old way wouldnt work with the GNOME Evolution 3.x that comes in Debian Wheezy. So, after a little digging around GtkHTML's sources, here..:
- Run 'gconf-editor'.
- Browse to "/desktop/gnome/interface/can_change_accels" and enable it.
- Browse to "/desktop/gnome/interface/gtk_key_theme" and set it to "Emacs".
- Start Evolution and open a new message. Hover your mouse over the 'menu items' whose key-bindings interfere with the normal Emacs world bindings (e.g: Print, Copy, Search, ...) and press "Del". This will 'unbind' those shortcuts from those menus. Close Evolution.
- Download this and put it in ~/.config/gtk-3.0/gtk.css
- Open a terminal and run:
$ gsettings set org.gnome.desktop.interface gtk-key-theme "Emacs"
$ chmod u-w ~/.gnome2/accels/evolution
- Enjoy "Ctrl+N", "Ctrl+P".. etc in the composer.