Edit Subject on Divi Contact Form (using add_filter)

edit_divi_contact_form_subject.php

<?php
/**
 * Edit Subject on Divi Contact Form (using add_filter)
 *
 * Divi contact form does not allow you to change the subject from the interface.
 * The problem is that on clients like Gmail the messages get threaded/organized under the same item/title.
 * To solve this we need a unique subject for each new contact.
 * However, Divi contact module does not have many hooks or filters, only allowing us to change the $headers[]
 * This would be great if the 'Subject:' was set on that variable, it is not, so we need to ADD a extra 'Subject:'
 * not an ideal solution, but it works and currently it is the only way to do this without editing the theme files.
 * 
 * Just add this code to your child-theme functions.php and you are set to go.
 * You can add extra variable like get_option('blogname') if you want.
 *
 * @author  António Pinto <apinto@vanguardly.com>
 * @license http://opensource.org/licenses/gpl-license.php GNU Public License
 * 
 */

add_filter('et_contact_page_headers', 'edit_divi_contact_form_subject', 10, 3);
   
function edit_divi_contact_form_subject($headers, $contact_name, $contact_email)
{
  $headers[] = 'Subject: New contact from the website ' . ' (' . $contact_email . ')';
  return $headers;
}