The Australian last line carries three elements and no punctuation: the suburb or locality, the state or territory abbreviation, and a four-digit postcode — MELBOURNE VIC 3000. The state abbreviation is not optional decoration. Australian suburb names repeat across states, so the abbreviation is what disambiguates them, and an address that drops it is genuinely ambiguous rather than merely untidy.
Four digits is also a shorter code than most international forms expect. A validator built around a five-digit US ZIP rejects every Australian postcode; one that pads to five digits corrupts them. And the leading digit is meaningful — it identifies the state or territory — so a code and a state abbreviation that disagree is a detectable error rather than something to accept quietly.
The unit of geography in the last line is a suburb, not a city. An address in a Melbourne suburb names the suburb, not Melbourne, which surprises forms that expect a city field to hold a recognisable city — the same class of mismatch that the United States has between USPS place names and municipalities, arriving through a different mechanism.
There is a second Australian convention that catches exports: the whole address is conventionally printed in capitals, not just the last line, and without punctuation. That is a presentation rule rather than a storage one — store what the customer typed — but a system that round-trips an address through an Australian carrier and then compares it to what it sent will find every field uppercased and read that as a change.
Australian addresses here are pinned to one of 15 real cities with a postal code genuinely issued for that place, with the street name and number invented. The phone number uses the Australian numbering plan's own trunk and length rules rather than a generic pattern, so it is structurally valid for the country it sits beside.