According to Milblogger Citizen Smash, one of the stories I linked to below is false: there is no general order preventing soldiers in Iraq from using e-mail, but rather a localized rule to stop GI's helping themselves to private bandwidth. According to Smash it's an example of how rumors get started:
It would appear that KBR contractors at Ginmar’s camp had set up their own wireless Internet system, and some industrious GIs have since set up their own unofficial Internet café, piggy-backing off the KBR system. But now the KBR folks are upset that the soldiers are slowing down their access (poor babies), so they’ve decided to end the “free ride.”
Not, he says, a general rule blocking access. Rather, the general rule was and remains that e-mail access is spotty, and mostly a matter of private enterprise.