A spokesman for police headquarters said: "We can confirm the email was written by NZ Police and sent to a number of people.
"NZ and Australian Police are currently seeking to establish how the email came to be public."
The spokesman said the email was in line with police practice to "regularly consult and liaise with law enforcement agencies around the world ... as a part of routine police business".
Security expert Dr Paul Buchanan of 36th Parallel Assessments said the step by police was "fairly pro forma for the cops" and shouldn't be seen as unusual.
He said at the point the request was made Wellington was bracing for a protest which some thought would lead to a repeat of the February occupation and it made sense to avoid adding to tensions with alt-right agitators being flown in from Australia.
The protest saw about 2000 people turn up for a protest march at which Destiny Church leader Brian Tamaki launched a new political movement. The protest saw a mock trial carried out which a disinformation expert said had "undertones of violent extremism".
Buchanan said he considered it reasonable for police to make a request of Australia law enforcement to look for information that could then be used to deny access to New Zealand on the grounds of bad character.
"We've got a lot of right-wing agitation. It really is a tense moment for the cops. I think some manager said 'we don't need these foreign guys turning up and stirring up s**t'. I think they were well within their rights."
Buchanan said the long delay between when Slater revealed the email and police making comment signalled recognition there was a "breach of security" and that "they are trying to find a mole".
"For something to be leaked to Slater would indicate the possibility there is someone who is ideologically akin or supportive of the actions of this guy.''
Slater was approached for comment, to which he said "f*** off".
The blogger suffered a massive credibility blow after the publication of the 2014 book Dirty Politics. Financial collapse followed, seeing him lose the Whaleoil website and go into bankruptcy. His bankruptcy period has recently ended.
Through a new website, Slater has provided a platform for those opposing public health measures and championed causes shared by those far to the right of the political spectrum.
Slater has painted Prime Minister Jacinda Ardern as an "evil tyrant" and pledged to "spend every waking moment working" to remove her from office.
The email from police in Wellington to Australian counterparts highlighted the imminent arrival of Avi Yemini and Rukshan Fernando who produce content for the right-wing website Rebel News.
Yemini purports to be a reporter but often presents information not supported by fact-checking.
It said: "NZ Police would like to stop the two from entering NZ and URGENTLY seek any information regarding criminal convictions or any information tending to show they are individuals of bad character, associated to criminal Groups and individuals or Far Right extremism groups".
When the pair tried to travel to New Zealand, Yemini was unable to do so.
Yemini, who has a conviction for domestic violence, had previously been refused entry to another country, providing grounds for him to be barred from New Zealand.
In the blogpost, Slater claimed the email showed "a deliberate political witch hunt against anyone who is deemed to be anti-government".
In the three days since the email emerged, it has been widely distributed on right-wing conspiracy courting websites totalling millions of followers.
In a piece on the new right-wing site The Platform, a "contributing writer" from Slater's site said it was leaked by "a trusted source" who had made contact to say "Police were lying and that documents existed to prove that".
The email has become the focus of a segment broadcast on Sky News Australia in which broadcaster Andrew Bolt called the email an "amazing development" in New Zealand's refusal to allow conspiracy theorist Avi Yemini into the country.
It has also seen conspiracy theorist Australian senator Ralph Babet issue a statement in which he accused New Zealand of being an "authoritarian regime".
Bolt said the email showed "New Zealand police shopping around in Australia for an excuse to ban Yemini".
