Copy to sender via Divi's contact form

functions.php

<?php
/**
 * Copy lines below into functions.php of your Divi child theme.
 */

add_filter( 'et_contact_page_headers', 'mycopytosender', 10, 4 );
function mycopytosender( $headers, $contact_name, $contact_email ) {
	$headers[] = "Cc: \"{$contact_name}\" <{$contact_email}>";
	return $headers;
}