Recently I was speaking to my local Courier Post driver (1-days contracted courier company). He was talking about 1Day and Torpedo7 so I asked how many "1-day" items he delivers each day on his run and he mentioned around 15 deliveries. I thought this seemed to be quite a high number of 1-day packages for one driver considering there must be hundreds of courier drivers each delivering around the same amount!
CourierPost have been unwilling to confirm how many drivers they have but from memory they have roughly 800 drivers nationwide. So we can guesstimate the volume of packages could be 800 x 15 = 12,000 per day. I think this could be a little high though because Ezibuy (the other major Mail-order company in New Zealand) and I remember about a year ago they were shipping 9,000 packages per day. So who is larger out of 1-day and EziBuy? I would say EziBuy are still the largest mail-order company. But I'm sure 1-day could soon overtake, as their range is far-reaching, and their prices are so low.