[WordPress] Customizing WooCommerce Emails

00-add-custom-line.php

<?php

add_action( 'woocommerce_email_before_order_table', 'acme_email_message', 20 );
/**
 * Adds a single line above the table of purchases in a WooCommerce email.
 */
function acme_email_message() {

	$html = '<p>';
		$html .= 'Access your additional information on your My Account page.';
	$html .= '</p>';

	$allowed_html = array(
		'p' => array(),
	);

	echo wp_kses( $html, $allowed_html );
}