/**
 * Use sendmail for sending the email
 *
 * @param   string  $sendmail  Path to sendmail [optional]
 *
 * @return  boolean  True on success
 *
 * @since   1.7.0
 */
public function useSendmail($sendmail = null)
{
    $this->Sendmail = $sendmail;
    if (!empty($this->Sendmail)) {
        $this->isSendmail();
        return true;
    } else {
        $this->isMail();
        return false;
    }
}