WooCommerce - Add custom field (in an order) to the order emails

gistfile1.php

/**
 * Add the field to order emails
 **/
add_filter('woocommerce_email_order_meta_keys', 'my_woocommerce_email_order_meta_keys');

function my_woocommerce_email_order_meta_keys( $keys ) {
	$keys['How did you hear about us?'] = 'hear_about_us';
	return $keys;
}

woocommerce_email_order_meta_keys - not properly!!!
woocommerce_email_customer_details_fields - properly!
//
add_filter('woocommerce_email_customer_details_fields', 'my_woocommerce_email_order_meta_keys', 10, 1);
function my_woocommerce_email_order_meta_keys($keys) {
$keys[] = 'you're text';
return $keys;
}

Can anyone see a problem with this? Any assistance much appreciated!

add_filter('woocommerce_email_order_meta_fields', 'custom_woocommerce_email_order_meta_fields', 10, 3 );
function custom_woocommerce_email_order_meta_fields( $fields, $sent_to_admin, $order ) {
$fields['delivery_date'] = array(
'label' => __( 'Pre-order' ),
'value' => get_post_meta( $order->id, 'delivery_date', true ),
);
$fields['message'] = array(
'label' => __( 'Message' ),
'value' => get_post_meta( $order->id, 'message', true ),
);
$fields['shipping_email'] = array(
'label' => __( 'Recipient Email' ),
'value' => get_post_meta( $order->id, 'shipping_email', true ),
);
$fields['delivery_instructions'] = array(
'label' => __( 'Special Delivery Instructions' ),
'value' => get_post_meta( $order->id, 'delivery_instructions', true ),
);
return $fields;
}

woocommerce_email_customer_details_fields doesn't work. I understand that woocommerce_email_order_meta_keys is depreciated, but it works...

Hi guys,

How can I implement this code to send the custom field in the "Admin New Order Email"?

@dimbert82
insert the code in your active theme or child theme functions.php

code like this:

add_filter( 'woocommerce_email_order_meta_fields', 'custom_order_mail_fields_callback', 10, 3 );
function custom_order_mail_fields_callback( $fields, $sent_to_admin, $order ) {    
        $fields['yourdata'] = array(
            'label' => __( 'yourdata to display' ),
            'value' => ' yourdata value',
        );
    }
    return $fields;
}