Comment # 5 on bug 1178596 from Fabian Vogt

Since
https://invent.kde.org/plasma/plasma-desktop/commit/d1f62c16c878a665c6e548f7a99b6fab21882e6d,
EmailClient can refer to a .desktop file instead.

xdg-email should do this in "open_kde":

if [ "$client" != "${client%.desktop}" ]; then
    client=`desktop_file_to_binary "$client"`
fi