The Illawarra postcodes which will drop back to letter deliveries every second day

Many posties will instead be diverted to driving vans to deliver parcels to help address the boom in online shopping as people visit shopping centres less often.

The changes are being rolled out across all metropolitan areas and the formula Australia Post uses means that all of the Wollongong, Shellharbour and Kiama local government areas will be affected.

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"While posties continue to deliver letters, this will temporarily change to be every second business day in all metropolitan locations only - there is no change to regional or rural area letter or parcel deliveries," an Australia Post spokeswoman said.

"Residents will be notified via a postcard delivered to their letterbox as this occurs in their area.

"Express Post, parcels and all post office box mail will continue to be delivered five days a week.

"These measures are part of temporary changes to Australia Post's performance standards, announced in April, in response to the operating constraints on our business due to the coronavirus pandemic and apply until 30 June 2021."

The Mercury asked Australia Post to confirm which postcodes would drop back to letter delivery every second day but its spokeswoman did not answer.

The every-second-day delivery scale-back applies only to "metropolitan areas". Australia Post says it is bound by a definition of metropolitan and rural areas contained in the Rural, Remote and Metropolitan Areas Classification from the 1991 Census.

And area with a population over 100,000 in the 1991 Census is classed as metropolitan. The classification system includes all three Illawarra local government areas in its "Wollongong statistical district" definition. This means although Kiama is not a city, and Shellharbour's population is about 72,000, they are classed as metropolitan.

"Additional Australia Post parcel delivery vans will hit the streets in Wollongong, Illawarra and Shoalhaven [this] week as some posties become temporary parcel posties to help deliver unprecedented parcel volumes and meet the changing needs of customers through COVID-19," the spokeswoman said.

Australia Post says its data showed the average household received the equivalent of one letter per week.

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