Note that in UK English if you start with Dear Sir or Dear Madam, you should end with Yours faithfully. But if you use the person’s name, you should end with Yours sincerely. This rule may seem arbitrary, but it is one of the rules of formal letter writing that is widely known in the UK; therefore I recommend you stick to it. However, there is no such strict rule in the US.

要注意在英式英语中，如果你的邮件以“尊敬的先生”或”尊敬的女士”开头，那应该以”你忠诚的……“结束。但如果你知道对方的名字，应该以”你真诚的……“的结束。这个规定似乎太武断了，但就是英国众所周知的正式邮件写法之一，所以我推荐你最好按照这个原则写。然而，美国没有这门严格的规定。

Here are some example closing sentences for emails:
这里有一些邮件结束语的例句：

I look forward to hearing from you.
我期待收到你的邮件。

I look forward to hearing from you soon.
我期待很快就收到回信。

I look forward to receiving your reply.
我期待不久就收到你的回复。

I look forward to seeing you.
我期待与你见面。

I look forward to meeting you.
我期待与你会面。

I look forward to speaking to you on this matter.
我期待和你探讨这个问题。

Please let me know a convenient time for us to meet.
请告知我方便见面的时间。

If you need any further information, please do not hesitate to contact me.
如果你需要进一步信息，马上联系我。

I will let you know more details as soon as I have them.
如果我有进一步消息，会马上通知你。

Please feel free to call me any time on my mobile: 0099 999 999 999
任何时候都可以打我手机，我的电话是：0099 999 999 999

I would appreciate your immediate attention to this matter.
如果您能马上关注这个问题，我将不胜感激。

As this matter is urgent, I would be grateful for a swift response.
考虑到这个问题很紧急，如果能尽快恢复我会很感激。