To grant an access permission to an attached file of an e-mail stored in a file server. An access permission to the attached file is set based on information included in a first e-mail. The attached file is stored in the file server. The second e-mail that is the first e-mail from which the added file is deleted and to which reference information for accessing the added file stored in the file server is added is transmitted to a receiver side mail server and a sender side mail server. In response to an access request to the attached file based on the reference information from either of a mail sender and a mail receiver, the file server controls the access to the attached file based on an access permission that was set.