"It is not part of a Corrections officer's role to send emails on behalf of a prisoner and exceptional circumstances would require consideration and approval from prison management as to the suitability of a request to do so," Pearse said.
"If necessary we will speak to the staff concerned and remind them of the correct process for prisoner correspondence."
Pearse said any further action against the officer would depend on the circumstances and would be determined by prison management.
"On rare occasions staff have been found to send an email on behalf of a prisoner, it is generally because the staff member involved is attempting to be helpful rather than anything more serious."
It was important for inmates to form and maintain connections with people in the community and positive relationships were invaluable, he said.
Inmates had a range of ways to keep in touch with family, friends, and support networks in the community including receiving emails, sending and receiving letters, and access to pay phones, with the prison also facilitating regular visits and video calls.
In May 2018 the 45-year-old Berrett was convicted following a jury trial of threatening to destroy property, attempting to pervert the course of justice, and two charges of blackmail.
During his trial evidence was given that he threatened to burn down an RSA, blackmailed an NZ Defence Force artist, and detailed an explosive attack on a Parliament building.
Berrett was sentenced in October 2018 to two years' intensive supervision and 180 hours' community work.
Despite applying to the Court of Appeal twice to have his convictions quashed, both appeals were declined, and Berrett has failed to carry out his sentence of community work.
Berrett was charged with failing to report to a probation officer in February 2020 and he was supposed to appear at Marton District Court in March 2020.
This resulted in Berrett's recent arrest but in a handwritten letter he appears to attempt to persuade the recipients he is being kept in the dark in relation to his incarceration.
"Since my arrest I have not appeared before a judge, I have had no legal counsel, I do not know what I am charged with, I do not know why I am being detained. I have not spoken with a lawyer, I received no information relating to my arrest.
"I am a mayoral candidate in this year's local body elections and my detainment is unlawful. It is undemocratic."
Corrections said it could take days to carry out the inquiries required to establish the circumstances around why the officer sent the email.
