A communication apparatus prepares a message including an image data address. A decision section in the communication apparatus compares the image data address with the destination address of the message and decides whether the recipient will be able to access image data stored at the image data address. If the decision is negative, a notification section notifies the operator of the communication apparatus. The operator can then cancel the message to avoid sending an image data address to a person who cannot access the image data, and take alternative action, such as reducing the size of the image data so that the image data can be included directly in the message.