What variables are available in notifications?

I’d like to customize the notification we receive when orders are placed.

How can I reference the email to use it in addition to SHIPPINGINFO

I see in helpers.php

$search_replace = array(
'CUSTOMERNAME' => $customer_name,
'ORDERID' => $order->get_id(),
'ORDERINFOSKU' => $order_info,
'ORDERINFO' => $order_info,
'SHIPPINGINFO' => $shipping_billing_info,
'PAYMENTINFO' => $payment_info,
'TOTAL' => $order_total,
'TRACKINGURL' => $tracking_url,
'ORDERNOTES' => $order_notes,

I need CUSTOMEREMAIL