Postcode validation

Written by Hylke Reitsma, co-founder of TouchDrop

Postcode validation is the process of verifying that a delivery address contains a valid Australian postcode that corresponds to the listed suburb and state. In direct mail, this is a critical step — postcards sent to incorrectly formatted or non-existent addresses are wasted spend.

Why postcode validation matters for direct mail

Australia has approximately 2,600 postcode areas across 8 states and territories. Each suburb-postcode combination must be consistent: you can't send mail to "Sydney NSW 3000" (3000 is Melbourne) or to a postcode that was never issued. Address errors that slip through validation result in undelivered mail — a cost with zero chance of return.

Beyond format errors, some Australian address types do not accept addressed marketing mail at all: parcel lockers (a PO Box-like Australia Post service), parcel collect points, and locked bag addresses.

What TouchDrop validates

Postcode-state consistency — The postcode must be a valid four-digit Australian postcode that belongs to the listed state
Parcel locker filtering — Addresses identified as parcel lockers are excluded (they don't accept addressed marketing mail)
Parcel collect filtering — Similar exclusion for Australia Post's parcel collect service addresses
Street number and name formatting — Basic format checks to catch obvious data entry errors

Australia Post address validation: the official route

Australia Post keeps the national list of every address it delivers to, the Postal Address File (PAF). It is released monthly and holds each address in its correct format together with a Delivery Point Identifier (DPID). Software that checks addresses against the PAF can be certified under Australia Post's Address Matching Approval System (AMAS). Certified software corrects the address to the PAF format and attaches its DPID, which is what the barcode on bulk-lodged mail is built from.

So a search for "Australia Post address validation" usually leads to AMAS-certified software or an address API built on it, not to a free lookup. To check a single address by hand, Australia Post's postcode search confirms that a suburb, state and postcode belong together. Facts checked against auspost.com.au on 26 September 2026.

Where address data comes from

In TouchDrop, address data comes from Shopify's customer and order records. The shipping address customers enter at checkout is used as the postcard delivery address. TouchDrop validates this data at the point of campaign audience assembly — before the postcard is queued for print — so invalid addresses are filtered without incurring a print cost.