和小秘沟通的邮件礼仪问题

LZ看过一些英文邮件礼仪的文章后，对一些细节还不太明白，想向大家求助。

问题情景如下：
lz向小秘发邮件询问成绩单和GT成绩是否收到：

Dear Sir or Madam,

My name is XXX and I have just submitted my application to your Ph.D. program in Statistics. My Applicant ID is XXX. I mailed my official transcripts and requested ETS to send my GRE & TOEFL score sheets to XXX weeks earlier, but I don't know whether they have been delivered successfully. Could you kindly check it for me, please?

I appreciate your taking the time to address my questions. I look forward to hearing from you.
Sincerely,
落款

小秘第一次回信：

Dear XXX,

I see official GRE scores but not TOEFL scores. We can use the unofficial scores for now while we wait for the official scores to arrive.

Best,

没有回答成绩单的问题，于是lz回复：

Dear Ms. XXX,

Thank you for your prompt reply. I also mailed my official transcripts including my college course work and diplomas from my school. I would greatly appreciate it if you could please tell me whether you have received these materials.
Sincerely

小秘回复：

Staff are working from home due to Covid. Next time I’m in the office I will check.

到这里，我还需要回复表示感谢吗？不回会不会不礼貌，回了会不会太啰嗦？如果回复，还需要加上Dear Ms. XXX的称呼吗，还是像小秘第二次回复一样简单一句话就可以？谢谢大家！

可以回可以不回，不影响什么。
礼貌回复单走一个Thanks加你的落款
不回复他也无所谓，小秘一天看几百封邮件，多数时候是记不得上下文的，你不回不必要的邮件，给他减少负担，也不是坏事。
(所以Re的时候带上前文内容很重要)

姓名称呼问题: 我自己习惯于第一封邮件就Dear Mr/Ms (last name)，后面如果对方以first namr称呼你，之后就可以Hi (first name)称呼对方了。

补充内容 (2020-12-3 02:31):
Mr/Ms可加可不加，取决于个人习惯
有title尽量加，比如prof, dr.之类的。

一般对于熟人可以直接Hi FirstName，对于不熟的可以Dear FirstName或者Dear [title] LastName (比如Dear Prof. XXX, Dear Dr. XXX，不过没太见过Dear Ms./Mr.)。对于楼主的情况应该不用回了，也是减少别人的工作量。