Recipient information is allocated to a transmission box in the image processing apparatus based on the header information in the e-mail sent from the external terminal. Scanned image data is stored and linked to the same transmission box. Subsequently, based on the recipient information, the image data is sent to the recipient as an attachment to an e-mail addressed to the recipient. Because the recipient information and the image data are linked via the transmission box, it is not necessary to simultaneously designate the recipient and input the image data. Therefore, the operation panel of the image processing apparatus need not be occupied for a long period of time.