Generate email on meta value update

WordPress triggers a custom hook when certain meta is updated, user meta counts. See updated_{$meta_type}_meta. Here’s an example use case:

add_action('updated_user_meta', function( $meta_id, $user_id, $meta_key, $_meta_value ) {
    switch ( $meta_key ) {
        case 'mobile_number':
        case 'address':

            $user = new \WP_User($user_id);

            // user
            wp_mail($user->user_email, 'Profile updated', 'Profile updated.');

            // admin
            wp_mail(get_bloginfo('admin_email'), 'Profile updated', "Profile updated for user {$user->display_name}.");
            break;
    } 
}, 0, 4);