"Emails addressed to an @horowhenua.govt.nz email address are the property of the Horowhenua District Council as is outlined in the Electronic Communication Policy," he said.
Mayor Michael Feyen said he was one of the people whose email communication had been intercepted, and he was extremely concerned by it.
He said the audit report, carried out in March by Manawatu Wanganui Local Authority Shared Services into all councils in the Horizons region had been "hidden" from him since then.
He said it took persistent emailing to get a copy, and that Mr Clapperton had called him and accused him of being the source of the document's release, which he was not.
He also claimed Mr Clapperton had demanded his resignation.
Former mayor Brendan Duffy confirmed the email interception had been occurring when he was in office before the local government election last October.
Both he and Mr Clapperton claimed the practice was to protect recipients from negative or abusive messages.
"If you saw the vitriolic messaging that some members of the community chose to send in, you reach a point where it is simply not tenable to continue to receive that sort of rubbish," Duffy said.
"There were occasions where I supported the decision to restrict the flow of messages that were, to my mind, entirely inappropriate."
Mr Clapperton said the interception was necessary "to protect my employees, so they can carry out their roles safely, without undue interference, inappropriate criticism and racist slurs".
He said that despite reports to the contrary, Mr Feyen, then a district councillor, was informed of the reasons for his emails being redirected.
"As well as this, all people and organisations who were sending the emails received an automatic reply stating that it was being redirected."
Fairfax Media reported emails that were blocked included those from Mr Feyen, an iwi representative, a ratepayers' association representative, a councillor and a former councillor.
An email with questions from one of their journalists to Mr Feyen was an example reproduced in the audit report, Fairfax said.
Mr Feyen said Mr Clapperton's justifications about safety were "utter crap".
"Nobody has got the right to do it," he said of the email interceptions.
"Especially unelected people withholding things elected people should be having."
He said he was concerned about the manipulation or omission of information to elected councillors that may have influenced decision making.
"Local government in New Zealand has to be really looked at, as the powerbase is not with the elected people, but with the unelected," he said.
Several other national groups have spoken up condemning the email vetting, including pro-democracy group Democracy Action, which released a statement saying that if the reported details were true, they constituted serious misconduct and warranted Mr Clapperton's resignation.
Deputy mayor Wayne Bishop issued a media statement on behalf of nine of Horowhenua's district councillors on Tuesday in support of Mr Clapperton, saying he was privy to the information in the report, and it was "not complete and outside the terms of reference".
He accused Mr Feyen of "an orchestrated campaign" to discredit the chief executive, said the media "failed to scrutinise" the mayor's commentary and suggested a by-election.
RNZ said the audit report also identified risk around the council's management of vehicle use, as well as with the governance of the chief executive.
NZME has requested the full contents of the audit report under the Official Information Act.
