1. letter; Including written letters, various official documents and contracts; All kinds of documents, statements (except blank statements), bills, securities (such as unused stamps, stamps, cards), etc. ; Various transactional notices; Various manuscripts; Various documents, etc.
2. Postcard: Postcard is a kind of card mail with communication nature, which is delivered in an open envelope. Postal enterprises at or above the county level may, with the approval of the provincial post office, print and distribute postcards printed with the words "China Post".