In order to facilitate updating of information on a destination of data, a data communication system includes a server and an MFP capable of communicating with each other. The MFP transmits to the server an update requesting signal including a source address of an e-mail received from another apparatus and related information on the source, transmits an address request to the server and receives user address data from the server, and transmits data to at least one destination address included in the received user address data. The server stores the user address data having destination addresses and related information on the destinations associated with each other, and in receipt of the update requesting signal from the MFP, rewrites the related information associated with the source address included in the update requesting signal by the user address data with the related information included in the update requesting signal.