It‘s in the bag
From the early days until the late 1980s, mail was traditionally carried in canvas bags. Between towns and cities, the mail was moved by trains that sometimes included a Railway Traveling Post Office, the last of which was withdrawn in 1971. Mail would often be picked up, sorted and dropped off en-route, sometimes without the train slowing down or stopping.
A loophole in the transport licensing rules at the time allowed for licensed bus services to also carry freight on scheduled routes; this saw a uniquely New Zealanddesigned bus that could carry goods at the back and passengers in the front; the composite. Ironically it was the Railways that operated many composite buses. Mail to and from overseas was also moved in canvas bags.
Photo: This picture shows three classic flat deck trucks of the 1950s and 1960s alongside the MV Wanganella in Wellington. Left to right they are: Bedford A, Ford Thames ET6 (Costcutter), and a Bedford OLB. From the ship‘s side the mail would be taken to the Overseas Mail Branch for sorting and distribution around the country by rail or composite bus.