"A covering letter will be attached to any found items which are re-delivered, so that customers are aware of what has happened."
NZ Post security advisor Julian Thorburn said the alleged thief was not an employee of the company.
"We became aware of it on Friday afternoon when the police notified us The majority of mail recovered appears to have been taken in the last year. The mail was taken after delivery from letterboxes and recycling bins," he said.
"Addressed items will be delivered next week with a letter of explanation attached."
So how could people protect their mail from thieves?
"Steps people can take to protect against theft after delivery include clearing mail regularly and installing a lock on their letterbox," said Mr Thorburn.
"If people are going away they should consider having their mail redirected, or setting up a hold on their mail."
Police said the find was a "great example" of the community and police working together to reduce inappropriate behaviour.
"It will be a positive outcome for those who have lost mail over recent months, even though they may be unaware in many cases," the officer said.
"Both police and NZ Post want to encourage residents to ensure they collect their mail on the new delivery days, and to report suspicious behaviour as soon as possible."