public function send($send_to, $body, $title=null)
    {
        $sender = static::getSender();
        
        $tos = StringHelper::toArray($send_to);
        foreach ($tos as $email) {
            $sender->addTo($email);
        }
        
        $subject = $title;
        if ($title) {
            if (strlen($title) > strlen($body)) {
                $subject = $body;
                $body = $title;
            }
        } else {
            $subject = StringHelper::str_cut($body, 15);
        }
        
        $res = $sender->setSubject($subject)->setBody($body, true)->send();
        
        if (!$res) {
            return ErrorInfo::error('mail send error, check error log');
        }
        
        return ErrorInfo::success('mail send success');
    }