An image data communication apparatus is connected to an image data source and to a network, and transmits 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 communication apparatus comprises a memory which stores a default mail address and a panel section which inputs a mail address of a user into the image data communication apparatus. The image data communication apparatus comprises a controller which sets the default mail address into the mail message of the e-mail to which the image data is attached when the mail address of the user is not input by the panel section, and 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 when the mail address of the user is input by the panel section. Thus, a reply to the e-mail is returned to the mail address of the user.