Depending on where you are in the (English speaking) world, the box outside your house or apartment for receiving letters might be known as a mailbox or letterbox, and the Chinese equivalent is just as simple:
The 信 （xìn） means letter and 箱（xiāng） is a box, easy enough. If we were taking about a postbox in the street, that anyone can use to send mail, then we’d use 郵筒（邮筒 yóu tǒng）- 郵（邮 yóu）means “mail” and a 筒子 is a “cylinder” or “tube” – I’m guessing because Taiwanese postboxes were traditionally cylindrical, just like the British and Japanese pillar boxes:
Rare Taiwanese Cylindrical Pillar Box (Source: Flickr)
Though the most common 郵筒（邮筒 yóu tǒng） that you’ll see in Taiwan are the box type, shown in the photo below:
These postboxes were found in an area in Kaohsiung, Taiwan that is scheduled for demolition and so has been decorated by the local school children.
Lastly, if you needed to weigh a parcel 包裹（bāo guǒ）before sending then you’d go to the post office, or 郵局（邮局 yóu jú）. Remember we said that 郵（邮 yóu） means “mail”? Well, 局（jú）is used for “office” – though not the kind of office that you’d do work in, that’s a 辦公室 （办公室 bàn gōng shì）. 局 is reserved for outposts of official organisations, such as the post office, or police station 警察局（jǐng chá jú） .
A post office in Taiwan