smtp设置自行参考手册说明
app/index/controller/Guestbook.php
90行后加
$list="";
foreach ($row as $key => $value) {
  $list.="".$key.":".$value."";
}
接着把
(new MsgSend())->send($config['msgemail'], $cate['title'], '有新的['.$cate['title'].']表单信息提交，请前往后台查看');
变更为
(new MsgSend())->send($config['msgemail'], $cate['title'], '有新的表单信息提交'.$list.'');