Change email format to display file name.

add_filter('dndcf7_before_send_files','cf7_custom_change_email_format', 10, 2 );
function cf7_custom_change_email_format( $links, $files ) {
    if( $files ) {
        $new_links = array();
        foreach( $files as $url ) {
            $new_links[] = wp_basename(  $url );
        }
        return $new_links;
    }
    return $links;
}