Corrections is setting up a "dedicated mail-monitoring team" following revelations the accused Christchurch shooter was able to send hate-filled letters from prison.
Corrections chief executive Christine Stevenson said an independent review was carried out by Miriam Dean CNZM QC and Grant O'Fee MNZM "immediately" after reports controversial letters had been sent.
Newshub revealed in August the alleged Christchurch massacre gunman Brenton Tarrant was able to send seven letters from prison, one which appeared to have a call to action for likeminded people.
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Multiple letters were also sent from Philip Arps, another white supremacist who was jailed for sharing Tarrant's livestream of the March 15 shooting.
Corrections admitted at the time that the letter seen by Newshub - in which Arps expressed his support for Adolf Hitler and openly talked of his disdain for the Prime Minister - should never have been sent.
The review found that while incoming mail processes work reasonably well, there were too many people involved in the outgoing mail processes.
It also found some prisons are not resourced well enough to manage this work given the sheer volume of mail. It's estimated around 15,000 items of mail are sent to and from prison each week.
Stevenson said she "made it clear" that she "did not have confidence in our existing processes for reviewing and assessing prisoners' mail" and "called for an immediate review into this practice" after Newshub's revelations.
She said she is now "confident the changes we are making as a result of the review will reduce the ability for mail sent and received to cause harm or distress, either directly or indirectly, to anyone".
As well as setting up a dedicated mail-monitoring team, Stevenson said regular audits of mail processes, including how staff make decisions to withhold or release mail, is being implemented.
Providing staff with interim guidelines on scanning and withholding mail, gang mail and content of a sexual nature was is also being taken on board, as well as providing prisoners with practical guidance on mail processes.
The review recommended 13 changes, and Corrections says it's still working on adopting four of them, including creating a new module on prisoners' communications in the training programme for new recruits.
Corrections is also working on providing advice to Corrections Minister Kelvin Davis on legislative changes to mail processes, and preparing new manual guidelines that are "clear, concise and take staff step by step".
Stevenson said until Corrections has confidence the new process is working, the mail of prisoners who have been identified with potential extremist ideologies and/or registered victims continues to be centralised.
"Public safety is paramount in every decision we make, and we will continue to work with our partner agencies to ensure we have the right skills, capability and experience to continually assess any threat that any prisoner or their correspondence poses."
Corrections announced in August that a 0800 number had been set up for people who receive unsolicited letters from prisoners, following Newshub's revelations.
Prime Minister Jacinda Ardern, who vowed not to speak the Christchurch-accused's name, said at the time there had "clearly" been a "systemic failure".
Corrections are legislatively required to manage prisoners in accordance with the Corrections Act 2004 and its international obligations for the treatment of all prisoners.
Sending mail is a required minimum entitlement under the Act.
