Laila Harre says the so-called Warner Bros email which alleged Prime Minister John Key was involved in a vast conspiracy to get Kim Dotcom could have been proved genuine if it had been properly tested.
She said she could not rule out that the email was real, even though the existence of it and the content of it was denied by every party referenced in it.
The claim has been backed by Dotcom, who told the Herald today he was "100%" convinced it was genuine.
In an interview with The Spinoff website, also published by the Herald, Harre talked in detail about her leadership of the Internet Party saying: "A month out I knew this was the wrong place to be. But by then I was committed. I was the captain of the Titanic and I had to stay with the ship."
For all her doubts about the party, she said "things would have been very different" if there had been an inquiry into the so-called email.
She also said "senior people" in Labour had asked her to stand for the party, a month after it became public she had rejoined it after 30 years of membership with other parties.
The issue around the email arose in the context of the Moment of Truth gathering organised by Dotcom in the Auckland Town Hall a week before the 2014 election.
Although not strictly an Internet Party event, it was the most high-profile event associated with the party in the lead up to voting.
Dotcom had promised a huge revelation at the meeting which would prove Key knew of his existence in New Zealand prior to the 2012 FBI-inspired raid which saw him and three others arrested.
The Prime Minister's knowledge of Dotcom's presence in New Zealand was a mainstay of the entrepreneur's belief his arrest and subsequent extradition request by the US were the fruit of a conspiracy in which Key was involved.
On the day of the Moment of Truth, the Herald received a copy of an email which purported to show Key had been involved in a conspiracy against Dotcom since at least 2010.
Then, having confirmed it was Dotcom's "big reveal", the Herald published the email and prompt denials that it was genuine from all parties named in it.
The publication of the email and the absolute denials that it was genuine appeared to have torpedoed it being produced at the Moment of Truth.
The Spinoff's Toby Manhire said to Harre the email "was almost certainly not authentic".
Harre replied: "I can't say that it was almost certainly not authentic."
She said Dotcom believed it to be authentic and she had formed a view based on the conversations she had at the time.
She said "if the provenance of it had been able to be tested in a kind of environment where people weren't at legal risk, then I think things would have been very different".
Harre claimed Key had avoided directly denying the meeting mentioned in the "email" was genuine.
"Even if you go back to John Key's reaction at the moment that came out was not to deny that this had taken place. It was to say you need to talk to my chief of staff about what happened at meetings.
"There was never a denial. And then the more powerful people, I guess, within the reporting class decided that this was something to go for, just to say it's not authentic."
In the lead up to the Moment of Truth, a decision on whether to use the email as part of the evening's revelations was changing "every hour in the couple of days before the event".
"When we went on stage, I believed that there was going to be a revelation, and that there was going to be a full explanation given of all this, which I believe would certainly have been convincing enough for those who could be convinced.
"But that didn't happen, so I'm still not quite sure when decisions were made and why, but, you know, Kim has taken a lot of risks on the legal side of his case, and I absolutely know that it was his lawyers and not him who were urging caution on this."
She said there was information held back. Asked what it was, she said: "The explanation for this email."
The Herald approached Dotcom on the issue today, receiving an emailed response. He said: "I'm 100% sure that the email is genuine. Unfortunately it was leaked without headers.
"My lawyers advised me against using it at the Moment of Truth. They suggested to use the courts, at the appropriate time, to seek discovery and depositions."
He said it had been difficult to get all the discovery which he believed was necessary for his case and was hoping to address that in a case before the Human Rights Tribunal shortly.
The so-called email was dated October 27, 2010 and was purported to be from Warner Brothers chairman and chief executive Kevin Tsujihara. The content of the so-called email claimed it had been sent to a senior executive at the Motion Picture Association of America - the lobby group for the Hollywood studios.
The alleged email stated: "We had a really good meeting with the Prime Minister. He's a fan and we're getting what we came for. Your groundwork in New Zealand is paying off. I see strong support for our anti-piracy effort.
"John Key told me in private that they are granting Dotcom residency despite pushback from officials about his criminal past. His AG will do everything in his power to assist us with our case. VIP treatment and then a one-way ticket to Virginia."
Warner Bros senior vice president for worldwide communications Paul McGuire said at the time: "Kevin Tsujihara did not write or send the alleged email, and he never had any such conversation with Prime Minister Key."
He said the statement - made two hours after the Herald first asked questions - came after a "thorough internal review".
He said: "The alleged email is a fabrication."
Contrary to Harre's recollection of events, Key stuck to his previously stated position that he had never heard of Dotcom prior to the 2012 raid. He said there was no conspiracy.
On the content of the email, he said he had absolutely no recollection or record of any such conversation. "I do not believe that to be correct. I have no recollection of the conversation alluded to in that email, there are no records there and the meetings I had were with other people around me."
The MPAA's Kate Bedingfield also dismissed the email. "Mike Ellis never received this alleged email or discussed this matter with Kevin Tsujihara."