In China, as in much of the world, the role of the physical 信箱 has changed dramatically. While once a daily checkpoint for personal letters and news, it's now more commonly used for official documents, utility bills, and bank statements. Package delivery, a massive industry in China, often uses dedicated parcel lockers (快递柜 - kuàidìguì) rather than personal mailboxes. The most significant cultural aspect of 信箱 today is its digital form. An email inbox (电子信箱 - diànzǐ xìnxiāng, often shortened to just 信箱) is a cornerstone of professional and academic life. However, for personal communication, messaging apps like WeChat (微信 - Wēixìn) have largely replaced both personal emails and physical letters. A subtle difference from suburban American culture is the physical mailbox setup. In Chinese cities, you won't typically find individual mailboxes at the end of a driveway. Instead, apartment buildings have a bank of small, locked 信箱 in the lobby or ground floor, one for each unit, reinforcing a sense of communal living space.
The use of 信箱 is heavily dependent on context.
The term is neutral and can be used in both formal and informal situations.