An image data communication apparatus is connected to an image data source and to a network, and transmitting image data attached to an e-mail to a receiving apparatus via the network. The e-mail including a mail from command and a mail message. The image data attached to the e-mail as an openable document. The image data communication apparatus comprises a panel section which inputs a mail address of a user to the image data communication apparatus. The image data communication apparatus comprises a controller which sets the mail address of the user input by the panel section into the mail message of the e-mail to which the image data is attached. Thus, a reply to the e-mail is returned to the mail address of the user.