I have tried using the following mailto:

mailto:[email protected]?subject=Info request for [custom_mailto_title]

and then this php:

add_shortcode( ‘custom_mailto_title’, ‘custom_mailto_title’ );
function custom_mailto_title( $atts ) {
return esc_attr( get_the_title( get_the_ID() ) );
}

It looks like it should work but it does not and my understanding of php is limited