Hollywood movie studio Warners Brothers is rubbishing Kim Dotcom's so-called 'bombshell' email evidence against Prime Minister John Key tonight as fake.

The email between Hollywood executives purports to show Mr Key was in on a plan to get Mr Dotcom extradited back to the US in 2010 on copyright charges.

But Mr Key has always insisted he never new about Mr Dotcom until just a day prior to the raid on his Coatesville mansion in 2012.

"We've checked all of our records and have all of them. I've got no recollection of ever hearing about the guy," Mr Key told reporters today.

But Mr Dotcom will try to prove otherwise tonight. And already an apparent four-year-old email has been leaked to the New Zealand Herald, allegedly written by Warner Brothers' chief executive to America's movie lobby group about Dotcom.

In the email, Warners' boss Kevin Tsujihara is alleged to say: "John Key told me in private that they are granting Dotcom residency despite pushback from officials about his criminal past.

"His AG (Attorney-General) will do everything in his power to assist us with our case. VIP treatment and then a one-way ticket to Virginia." Virginia is the home of the CIA.

"I do not believe that to be correct," Mr Key said. "I have no recollection of the conversation that's alluded to in that email. There are no records there and the meetings I had were with other people around me."

A spokesman for Warner Brothers this afternoon said: "Kevin Tsujihara did not write or send the alleged email, and he never had any such conversation with Prime Minister Key."

Greens co leader Russel Norman says the email should have been released a long time ago.

"Whoever was sitting on it, I just think if it's a legitimate email, if it's true, it should have been public a long time ago."

Mr Dotcom claims officials gave him residency as part of the controversial The Hobbit deal cut between the Government and Warner Brothers. Mr Dotcom is suggesting that by getting residency in a friendly country like New Zealand, US officials would find it easier to extradite him.

Mr Key, asked was he in on the plan to have Kim Dotcom extradited to the US, replied: "No."