I did a bit more research and this is what is working for me now.
The admin will only get an update if a pending post is added or updated.
add_action( 'transition_post_status', 'pending_post_status', 10, 3 );
function pending_post_status( $new_status, $old_status, $post ) {
if ( $new_status === "pending" ) {
$post_title = get_the_title( $post_id );
$post_url = get_permalink( $post_id );
$subject="A post has been updated";
$message = "A post has been updated on your website:\n\n";
$message .= "<a href="". $post_url. "">" .$post_title. "</a>\n\n";
//send email to admin
wp_mail( '[email protected]' , $subject, $message );
}
}