codeigniter中的电子邮件首选项不起作用

这是我的邮件发送代码

函数send_letter ()

{
    $config['mailtype'] = 'text or html';
    $this->email->initialize($config);
    $description =  $this->input->post('description',true);
    $subject =  $this->input->post('subject',true);
    $this->load->model('newsletter_model');
    $this->data['mail_list'] = $this->newsletter_model->getmaillist();
    foreach($this->data['mail_list'] as $val)
    {
        $this->email->from('dfdf1@gmail.com', 'Imageinit');
        $this->email->subject($subject);
        $this->email->message($description);
        $this->email->set_newline("'r'n");
        $this->email->to($val['emailid']);
        $this->email->send();
    }  
    $newdata=array('success'=>1);
    $this->session->set_userdata($newdata);
    $this->index();
}

邮件发送成功，但当我发送html数据邮件也包含html数据

如. .如果我用粗体标签发送数据，它会显示粗体标签。不使文本加粗