The first is in the beginning of the letter.
In Chinese business letters, as in other culture's letters, the recipient's name is also on a separate line at the top. But we can also add these following honorifics for formal letters, for example: 尊敬的 zūn jìng de (honorific)，敬爱的 jìng ài de (respected).Of course, many business letters can be somewhat informal for those with whom you have an established "first name" relationship. For example, if you want to write an email to your boss, you can use the "尊敬的+…"(here is the name), and then followed by the colon.
Next is the body of the letter.
In China, we have to say "hello" in the beginning: 您好 nín hǎo or 你好 nǐ hǎo. (However, this is not the case in other cultures. In fact, in US American business letters writing, it is considered inappropriate to start a letter this way!) Now, for example, we want to call the opposite company, how should we write? The answer is: 贵公司 guì gōng sī, that is in front of the company with "贵" In Chinese ("贵" is also used for asking somebody's age). Namely: 贵庚 guì gēng. This is an expression of respect. We can say"我方 wǒ fāng"for" our company" ; "敬请谅解 jìng qǐng liàng jiě (please understand)" can be used when we want somebody to understand a situation of something ; "特此致歉 tè cǐ zhì qiàn (Sincere apology)" can be used to write for specifically apologizing for something; "不胜感激 bú shèng gǎn jī (Thanks a lot)" can be used to express gratitude.
The close of the letter.
Since the relationship between persons is different, the content of each letter is different, so the closing of the letter likely will be different. Here are some examples, such as "特此函达 tè cǐ hán dá (hereby informed)，即希函复 jí xī hán fù (looking forward for your kind reply)." Also written to express the good wish such as "此致敬礼 cǐ zhì jìng lǐ (with high respect)" "敬祝健康 jìng zhù jiàn kāng (wish you health)" "望一切顺利 wàng yí qiè shun lì (best regards)" and so on.
In addition, the signature on a letter should be the person's full name and title. For example, we can write it as "the secretary of ×× company + the name." (Usually Chinese names are written on another line which is after the end of the letter after skipping one or two lines, and on the lower right side. But in general the signing of the of a business email can be also on left side.) In addition, the date must be accurate, showing the writer is responsible for this. (The date is normally written on the line of the signature or on the right side of another line.)
Well, the above content is just a brief introduction about Chinese business email. You can get more details about it by taking the business Chinese course.