The authenticity of the email will either point to Rudd or Swan, or both, misleading the Parliament, or not. If the email is a fake, as the Government is claiming, then Opposition Leader Malcolm Turnbull's integrity in pursuing the matter may also be under question.

And Rudd is calling the bluff. He has brought in the Australian Federal police over the matter.

The import of the email is such: whether or not Swan or Rudd made personal representations on behalf of prominent Ipswich car dealer John Grant's inquiries into the OzCar financial support scheme. Both have denied any political favouritism.

Backing up just a little, Grant is a long-time friend and neighbour of Rudd. Indeed, he donated a second-hand ute to Rudd to use during his election campaign. Swan knows Grant, also, but yesterday qualified the association by saying he had once bought a second-hand car off him.

Backing up just a little more, Grant has not benefited from the OzCar scheme. And he has pointed out in the media that being a friend of Rudd's should not preclude him from making legitimate inquiries into a scheme that could help his business during the global financial crisis.

So where does this leave the public?

Whether or not to believe an email is fake.

Turnbull, while calling for Swan's resignation yesterday, insisted he had not seen the email, nor had any members of his party; that no Liberal Party member had leaked the email to the media; or fabricated it.

Rudd's office, meanwhile, launched an investigation into the email, had IT specialists check for the email, and insisted ''there is no email''.

The whole email sensation, then, comes down to the most intriguing of elements in the story; that of the comments made by the Treasury official in charge of the OzCar scheme, Godwin Grech. Confused, distressed, he told Friday's estimates committee hearing that he recalled an email, but could be mistaken. He conceded he had the impression Grant was ''more than your usual constituent''.