A file storage system that allows the user to easily designate a desired location to store a file is configured as follows. In response to a tree structure request mail from a client, a server creates a tree structure for a folder that can be accessed by the user, and describes it in a mail for reply. The user receives the mail with the description of the tree structure, designates a storage location in the form of a reply thereto, and sends a mail with an attached file to be stored to the server. Upon receiving this mail, the server stores the attached file in the designated storage location.