Radio host Noelle McCarthy has been accused of being "nasty and bitchy" after the departure of a Radio New Zealand colleague.

McCarthy's private account was commandeered and an exchange, in which she attacked her former producer, was forwarded to her colleagues and leaked to media outlets.

McCarthy's bosses at the state broadcaster are defending their host "100 per cent" and said the leaking was motivated by malice. Radio NZ similarly backed McCarthy when she faced allegations of plagiarism in 2008.

The Irish-born radio host, 31, began her broadcast career at Auckland student radio station bFM, before being contracted by Radio NZ National to fill in for Jim Mora on his afternoon show, and to host Summer Noelle through December and January.

The leaked emails concern the departure of producer Meredith McGrath, who begins work as a publicist for book publisher Hachette tomorrow.

The exchange between McCarthy and Janet Wilson, a media adviser to Supercity mayoral candidate John Banks, includes this from Wilson:

"That's the best birthday present a girl could hope for. You saw her off girlfriend ..."

Discussing McGrath's future, McCarthy wrote that her next stop could be hell: "Shovelling cinders with Satan's minions?"

Asked for comment yesterday, McGrath said the exchange about her was "nasty and bitchy".

She said she was not the source of the leak and did not want to comment about her working relationship with McCarthy.

"I don't want to engage in any tit-for-tat in response to emails through the media. I have moved beyond Noelle now."

McCarthy said the correspondence was private and not meant for public consumption. She was shocked to learn it had been widely leaked:

"It's beyond fair play, it's beyond human nature - I can't believe anyone would act like that. It's a violation."

She suspected someone at Radio NZ had been responsible and accessed her computer.

McCarthy accepted that some of her writing could be construed as mean-spirited, but said the motive of the leaker was to portray her that way.

"I think that's very much the intention, to make me look like a mean person."

Wilson also said the correspondence was private and should have remained so. H

achette general manager Kevin Chapman said he was aware of bad blood between McGrath and McCarthy, but learned of the leaked exchange only yesterday.

He took umbrage at Wilson's description of Hachette as the "cheap and cheerful publishers of this parish".

"Of last year's Booker shortlist, one-third of them were out of our stable," he said.

Wilson retorted: "If Hachette feel they are upset by this, in what is a casual conversation between two friends, they should grow up."

Radio New Zealand network manager John Howson said his organisation backed McCarthy 100 per cent and viewed the leak as "pretty nasty".

The leaker had not been identified because the sender used a dummy Gmail account.

"Who would go to the trouble of creating that," he asked. "We'd be very interested in knowing."