PHPMailer::addCustomHeader PHP Method

    public function addCustomHeader($name, $value = null)
    {
        if ($value === null) {
            // Value passed in as name:value
            $this->CustomHeader[] = explode(':', $name, 2);
        } else {
            $this->CustomHeader[] = array($name, $value);
        }
    }

 /**
  * Inner mailer initialization from set variables
  *
  * @return void
  */
 protected function initMailFromSet()
 {
     $this->mail->setLanguage($this->get('langLocale'), $this->get('langPath'));
     $this->mail->CharSet = $this->get('charset');
     $this->mail->From = $this->get('from');
     $this->mail->FromName = $this->get('fromName') ?: $this->get('from');
     $this->mail->Sender = $this->get('from');
     $this->mail->clearAllRecipients();
     $this->mail->clearAttachments();
     $this->mail->clearCustomHeaders();
     $emails = explode(static::MAIL_SEPARATOR, $this->get('to'));
     foreach ($emails as $email) {
         $this->mail->addAddress($email);
     }
     $this->mail->Subject = $this->get('subject');
     $this->mail->AltBody = $this->createAltBody($this->get('body'));
     $this->mail->Body = $this->get('body');
     // add custom headers
     foreach ($this->get('customHeaders') as $header) {
         $this->mail->addCustomHeader($header);
     }
     if (is_array($this->get('images'))) {
         foreach ($this->get('images') as $image) {
             // Append to $attachment array
             $this->mail->addEmbeddedImage($image['path'], $image['name'] . '@mail.lc', $image['name'], 'base64', $image['mime']);
         }
     }
 }