 By 1968, 75% of mail was using postcodes, and in the same year post office preferred-size envelopes were introduced, which came to be referred to as “standard envelopes”.Postcode squares were introduced in June 1990 to enable Australia Post to use optical character recognition (OCR) software in its mail sorting machines to automatically and more quickly sort mail by postcodes.Australian postcodes consist of four digits), and are written after the name of the city, suburb, or town, and the state or territory