Disclosed herein as a preferred embodiment is an image forming apparatus for printing data requested to be printed from a client apparatus via a network. The image forming apparatus comprising determination means for determining whether or not an instruction string is described in the body portion of e-mail sent from the client apparatus and controlling means for, in the case where the determination means determines that the instruction string is described, printing the data contained in an attached file according to the instruction string. And a control program, a method and a system for controlling these are also disclosed.