Hi,
to send an email when Advert is saved in the database as pending you can use the advert_tmp_to_pending post status transition like this
add_action( "advert_tmp_to_pending", "on_advert_pending", 10, 1 );
function on_advert_pending( $post ) {
$to = get_post_meta( $post->ID, "adverts_email", true );
$subject = "New Ad has been posted.";
$msg = sprintf( "You can view your Ad here %s", get_permalink( $post->ID ) );
wp_mail( $to, $subject, $msg );
}