The email, dated October 27, 2010, purports to be from Warner Brothers chairman and chief executive Kevin Tsujihara to a senior executive at the Motion Picture Association of America - the lobby group for the Hollywood studios.
However, Warner Bros told the Herald yesterday the email was a fake. Paul McGuire, the movie studio's senior vice president for worldwide communications, told the Herald: "Kevin Tsujihara did not write or send the alleged email, and he never had any such conversation with Prime Minister Key."
The evening saw the audience transfixed by a series of disclosures from journalist Glenn Greenwald, his source Edward Snowden and WikiLeaks founder Julian Assange.
But the international guests could not paper over the absence of Dotcom's promised evidence.
Towards the end, there was a passing reference by Dotcom's international lawyer Robert Amsterdam to an email which purported to prove the conspiracy.
Ms Harre told TV3's Firstline programme this morning the email "provides very clear evidence that the Prime Minister did know about the existence of Kim Dotcom and more than that, that he was involved very intimately with the process of this case."
"I have no doubt that Kim is absolutely truthful about that email.
"There needs to be a proper process now to investigate that."
Asked why Dotcom declined to comment on the email last night, Ms Harre said he'd received legal advice not to do so.
"The strong advice to him was to make sure that this evidence was put before a proper judicial process. That is what Parliament's privileges committee is.
"He followed the advice, rather than his gut instinct to share everything yesterday.
In a press conference after last night's event, Dotcom stood by the email. "I believe it to be 100 per cent true."
Told it had been labelled fake, he asked: "What alternative do they have? The Government lies all the time."
But it didn't stop more questions from journalists, leaving Dotcom trying to point the media to the issue of mass surveillance.
"[The public] don't care about my case tonight. They care about being subjected to this evil mass surveillance."
Finally, he appeared to lose his cool and angrily lectured the media: "You have an obligation after what you have learned tonight to take the information you have learned from Glenn Greenwald.
"You have failed New Zealanders in the past -- look at Dirty Politics," he said, referring to the book about the alleged National Party attack politics campaign. "You need to wake up and do your jobs.
"My case only affects me. It doesn't matter tonight. That's why we didn't make a big deal out of it. You need to get your priorities right. We have focused on the much bigger lie, which is every single New Zealander subjected to mass surveillance."