The word 邮件 is formed through a conceptual combination of two meaningful characters: 邮 (yóu), which carries the core idea of "postal" or "mail-related" matters, and 件 (jiàn), which denotes a "piece", "item", or "document". By placing them together, the composite meaning naturally emerges as "a postal item" or "a piece of mail". This formation directly extends in modern usage to mean "email", where the first character retains its core concept of "sending communications" and the second character continues to indicate a discrete unit or message.