When creating cXML PO, how do I populate buyer email address in the cXML file sent to the supplier?

We are using Oracle EBS 12.1.3.  We are creating a Purchase Order by punching out to supplier's site to go shopping, returning contents of the shopping cart back to Oracle to create/appove the Requisition and then auto-create/approve the PO, and then generate the cXML file for Direct Transmission to the Supplier using OTA.  We want the supplier to send acknowledgement back to the buyer via email … so we need to populate the buyer's email address in the email field in thecXML file.  How do we do this?

In the <OrderRequestHeader> section … there is a <Contact> sub-section.

In this sub-section … there is a field called <Email>.