I'll draft a letter for you.

我来为你草拟一封信。

《牛津词典》

There's a letter for you.

有你一封信。

《牛津词典》

There's a letter for you from your mother.

有你母亲的一封来信。

《牛津词典》

"They help you do your resume, your cover letter and everything you need for a job interview, and they help you find a job whatever you're interested in."

VOA: special.2010.05.13

You remember the "Letter to a Friend" that we looked at for the last time.

你们记得上节课我们读的《信朋友的一封信》吧。

耶鲁公开课 - 弥尔顿课程节选

Could you tell us about a person who wrote a recommendation letter for you?

你能给我们介绍一位给你写推荐信的人吗？

写推荐书的人 - SpeakingMax英语口语达人

In response to a demand for payment, a short letter simply telling them that you cannot pay now is light years better than ignoring the demand letter.

FORBES: Five Ways To Pay Your Taxes When You Don't Have The Cash

But if the tenant wants to bring a dog, you have a right to ask for a letter from a therapist or doctor that explains why the animal is necessary to use and enjoy the unit.

WSJ: Should 'Support Dogs' Be Allowed in No-Pets Buildings?--WSJ House Talk

When the response rate is slower than a letter, you wonder what social is for.

FORBES: Welcome to The World of Protest in The Age Of Social Media