An image input/output system is used to input information for specifying the transmission source of data and a period of time during which the data should be received as search conditions for specifying the data that should be received. On the basis of the input conditions, the reception history of the data received via a network or a public network is read. The reception history is searched to determine whether the data that should be received has already been received. On the basis of the determination result, when the data that should be received has not been received, the fact that the data has not been received is reported.