It could take three more weeks for the backlog of mail in Christchurch to be cleared.
New Zealand Post resumed deliveries on Tuesday despite still dealing with its own infrastructure problems.
Although it is voluntary for New Zealand Post staff to work, about 90% are turning up to their jobs.
New Zealand Post has carried out reconnaissance runs to see which routes are capable of deliveries, and has found crews can reach only about 60% of the city.
The most significant problems are in the south and east of the city. One of New Zealand Post's six delivery branches, Ferrymead, has been closed.
Delivery manager Matthew Riordan says mail due for delivery on the day of the quake is only now going out.
He says delivery staff are having to wear safety glasses and face masks because of the dust in the city.