wcmo_registration_approval_message.php

<?php
function prefix_external_registration_approval_message( $message, $url, $user_id ) {

	if( ! apply_filters( 'wcmo_allow_external_approval', false ) ) {
		return $message;
	}
	$user_data = get_userdata( $user_id );
	$message .= '<p>User email: ' . $user_data->user_email . '</p>';
	
	return $message;
}
add_filter( 'wcmo_registration_approval_message', 'prefix_external_registration_approval_message', 100, 3 );