Insert this code into your site, then use the smartcode in the snippet and add it as a default field in a hidden field. Then add that field to the email notification settings.
/*
* Use default value in the editor as
* {embed_post_author_email}
* Then it will show the embeded post's author email
*/
add_filter('fluentform_editor_shortcode_callback_embed_post_author_email', function ($code) {
return get_the_author_meta('user_email');
});