1. A job executing device, comprising: an image-reading unit of reading an image of a physical document; a job executing unit of executing a job concerning image data; an execution instruction-receiving unit of receiving an instruction for job execution sent to the job executing unit by a user authenticated by an authentication unit; a memory unit of storing a notification destination corresponding to user identification information inputted for user authentication; and a notification unit of transmitting an electronic mail message, after the job is executed according to the received instruction for job execution, to the notification destination corresponding to the inputted user identification information; wherein the electronic mail message displays a notification that the job has been executed and includes a button to send reply information to the job executing device indicating that the inputted user identification information cannot be used for user authentication so that a user seeking to execute a future job, after the job is executed, cannot use the inputted user identification information to instruct execution of the future job.