To provide a method and a system that can easily enclose transmission items for customers, each of which is independently controlled by several custom er information systems.

The enclosing item information management system 16 asigns common identification data, that include customer information and addressee information to each addressee data, that is sent from each independently controlled customer information management system 10-12 to the enclosing information system and stored in a storage device 16a. The enclosing information system 16 automatically merges each customer transmission item information with each customer, who is identical with the addressee on the basis of the common identification data stored and generates the enclosed item management data to control the enclosed documents by an addressee unit. Thus, the information system consolidates the customer mailing documents with the customers, who are identical with addressees as the one transmission unit, by referring to the generated enclosed document management information.