Please address the envelope before mailing the letter.

寄信前，请在信封上写上地址。

youdao

Once you have decided to send, you then have to determine who to include on your list, what kind of business greeting card to choose, and how to address the envelope.

一旦你决定寄出的话，你需要决定你的清单上包括哪些名单，挑选哪种类型的商务贺卡，还有怎么样让信封看起来有意思。

youdao

The address must be clearly visible through the window of the envelope.

从信封的透明窗必须能够看清楚地址。

《牛津词典》

He said the equivalent in the nonelectronic world would be a catalog that is sent to a home in an envelope with the ability to send out the recipient's address to other stores the minute the envelope is opened.

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They stick them onto a special envelope and write the address they want it posted to.

BBC: The extreme stamp collecting of first day covers

The handwriting was close to that on the Daschle and Brokaw letters, and the return address on the letter was to an elementary school in New Jersey -- just like on the envelope to Daschle.

CNN: letters