I am writing to you in connection with your recent job application.

我写此信与你最近求职一事有关。

《牛津词典》

I am writing to express my sincere gratitude for your help in my study.

我写这封信是为了感谢你在学习上对我的帮助。

youdao

I am writing to you concerning the Bernster Special 150 SL that I bought from you two weeks ago.

我给您写信是关于我两周前从您那里购买的 Bernster Special 150 SL。

youdao

Well, for a thing called main which itself is a function but a function I wrote, a tool I am writing at the moment not like printf which someone else wrote long ago, I have to say where does main start, where does main end, and I do that by using these curly braces.

至于这个名曰main的函数,由我们自己写的函数，也是一个工具,只不过由我们自己编写，而不是像printf那样已经由前人写好了,我们必须要说明main在哪开始，在哪结束，这样我们就要用到大括号了。

哈佛公开课 - 计算机科学课程节选

Or if I am writing to complain about an embarrassing situation that happened at a hotel.

BBC: E-mail: Who's reading yours?

"I am writing to ask you to STOP gun violence, " wrote Tajeah, a 10-year-old from Georgia.

NPR: In Letters, Children Ask Obama To Change Gun Laws

So, today, I am writing to spread the word about an attempt to reach our families in their homes.

FORBES: Parents and Teachers: Join National Money Talk Night