protected function get_mail_type()
	{
		$return = $this->config['is_html'] ? 'html' : 'plain' ;
		$alt = trim($this->alt_body);
		$return .= ($this->config['is_html'] and ! empty($alt)) ? '_alt' : '';
		$return .= ($this->config['is_html'] and count($this->attachments['inline'])) ? '_inline' : '';
		$return .= (count($this->attachments['attachment'])) ? '_attach' : '';
		return $return;
	}