New Zealand Post says as many as 20,000 pieces of mail have been hoarded and not delivered by a contractor in Queenstown.
A contractor in Queenstown is facing charges of theft. Thousands more items of unopened mail were found on Thursday.
New Zealand Post communications manager Michael Tull told Morning Report the company began investigating complaints of undelivered mail in the suburb of Fernhill a year ago.
But the investigation intensified when more mail went missing in August.
NZ Post hopes to begin delivering items of unopened mail in the next week.