The issue may be in the neomutt.desktop file: [Desktop Entry] Categories=Office;Network;Email; Comment=Simple text-based Mail User Agent Comment[de]=Einfaches, Text-basiertes Mailprogramm Exec=neomutt %u Icon=neomutt Name=neomutt Name[de]=Mutt MimeType=x-scheme-handler/mailto; NoDisplay=false Terminal=true Type=Application
Terminal=true specifies that this mailto scheme-handler runs in a terminal, but finding out what terminal to use is left completely up to the desktop environment, which can vary a lot depending on if the user is even using a desktop environment. One possible workaround could be to use Debian's x-terminal-emulator symlink like this: Exec=x-terminal-emulator -e neomutt %u Terminal=false
