WooCommerce: debug emails, output mail id

add_action( 'woocommerce_email_order_details', 'get_the_wc_email_id', 9, 4 );
function get_the_wc_email_id( $order, $sent_to_admin, $plain_text, $email ) {
    // Will output the email id for the current notification
    echo '<pre>'; print_r($email->id); echo '</pre>'; 
}