The New Zealand Post Office was a New Zealand government department. As a Government Department, the New Zealand Post Office or N.Z.P.O., previously the Post and Telegraph Department or P & T, had as the political head the Postmaster General who was a member of Cabinet, and, when it was a separate department the Minister of Telegraphs. The N.Z.P.O. was similar to the British Post Office or GPO, and so was similar to European PTT or postal, telegraph and telephone services, which were government monopolies.

History
19th century
The first official Post Office in New Zealand was opened in 1840 when Captain Hobson, the newly appointed Lieutenant-Governor, arrived in the Bay of Islands and appointed William Clayton Hayes as Clerk to the Bench of Magistrates and Postmaster. Within six months, Hayes was suspended from duty – the first civil servant to incur this penalty in New Zealand – for neglect of duty and continual inebriety.
The establishment of settlements across North and South Islands meant the need for an internal postal service was becoming more and more important, however New Zealand's geography, and ongoing wars between Maori and Europeans and inter-tribal fighting hindered communication. At the time, shipping mail coast-to-coast, although inefficient, was the most reliable means of transporting mail around the country. A monthly shipping service to Sydney, where mail was exchanged with outbound and inbound London ships saw the first regular overseas mail service established.
The Local Posts Act of 1856 and the Post Office Act of 1858 signalled a period of growth for the New Zealand Post Office. The Local Posts Act gave provincial councils the authority to create their own mail services and local Post Offices, while the Government continued to maintain the overland trunk postal routes and the head Post Office in each province. The Post Office Act repealed the Local Posts Act, establishing the Post Office as a separate government department, reporting to the Postmaster General, and providing for its administration.
By 1880 there were over 850 post offices. The following year, the merger of the Electric Telegraphs Department with the Post Office Department created the enlarged New Zealand Post and Telegraph Department, which later became the New Zealand Post Office.

20th century
The New Zealand Post Office entered the 20th century as a burgeoning government department with over 1,700 branches.
Rapid growth of the Post Office continued throughout the century, with its broad role as post office, savings bank and telephone exchange cementing its place in New Zealand society. Public demand for its services, including the growth of private telephones in people's homes, and the introduction of internal and international airmail services in the 1930s, enabling faster, more efficient mail services, ensured its future.
By the middle of the century, the Post Office was a complex and financially successful organisation – fulfilling political, social and economic needs. Its role in the community was expansive. Beyond the traditional communication services, the Post Office provided important community services including registering births, marriages, deaths and cars, accepting television and fishing licence fees, enrolling people to vote, and collecting pensions. Post Offices also provided daily weather and temperature checks for the Meteorological Office, and postmasters were able to perform marriage ceremonies.
In the 1960s and 70s steps were taken towards better managing the ever-increasing volumes of national and international mail: the installation of New Zealand's first mechanical mail sorting machine in the Auckland parcel depot, and the introduction of address postal codes to simplify bulk mail sorting. However, increasingly the tension between political and commercial pressures meant the business was not operating efficiently.
By the 1980s, the variety of roles, the sometimes-conflicting needs of three different businesses, and political considerations were major constraints on the Post Office. It was increasingly unable to meet growing consumer demands and the postal side alone was losing over $20 million a year, with expectations that this would balloon in the future.
In 1985, Jonathan Hunt, Postmaster General, ordered a review of the organisational and management structure of the Post Office. The subsequent Mason-Morris report of 1986 called for sweeping changes, separating the three core businesses to operate as independent State-owned corporations.

Abolishment
On 1 April 1987, the department was abolished under the Postal Services Act 1987, and three state-owned enterprises (SOEs) were formed:
New Zealand Post Limited
Telecom New Zealand Limited
Post Office Bank Limited
Of these, due to privatisation, only New Zealand Post remains as an SOE. Telecom was sold to two United States Baby Bells, and PostBank was sold to the Pacific banking conglomerate Australia and New Zealand Banking Group (ANZ). The PostBank brand was phased out by the late-1990s.
Later on, as per the conditions of Telecom's privatisation, it was floated in the early 1990s on the New Zealand Stock Exchange.