<?php
// Do NOT include the opening php tag shown above. Copy the code shown below.

add_filter( 'woocommerce_email_order_meta_keys', 'wpdesk_vat_number_display_email' );
/**
* VAT Number in emails
*/
function wpdesk_vat_number_display_email( $keys ) {
     $keys['VAT Number'] = '_vat_number';
     return $keys;
}