Send ordinary letters into a roadside mailbox. Someone will take it out.

寄普通信只要投到路边的信筒里就好了，会有人去取的。

youdao

These letters can be dropped in any mailbox in China and will be kept by China Post for 10 years.

这些信件可以投递到中国境内任何一个邮政信筒，中国邮政会统一将它们封存10年。

youdao

He hastened to start up computer, to login his mailbox in Chinese website of yahoo, which is used specially to receive letters from China and is only known by his Chinese friends.

他迫不及待地打开电脑。登入雅虎中文网站的电子信箱，这个电子邮件地址是他专门用来收录来自中国的电子信件的，只有中国的朋友知道他这个电子邮件地址。

youdao

But they do have their letters, and that mailbox, and some pretty convoluted plot twists to keep them company as they bob like corks on a stormy sea of time... or something.

NPR: Double Feature: Playing with Words, and Time

It's been a few days since we read from your letters, so let's dip into the mailbox.

NPR: Letters: ICE Raid in Iowa; 'Hockey Night' Song