The BillingPostCode is a mandatory field. If the customer is not based in the UK, a dummy postcode may be sent to Sage Pay. When a customer selects a country outside of the UK, you may format the postcode with 000.
Sage Pay respond to each transaction with the status of the transaction along with the address/postcode results.
In MySagePay, if you were to manually double click on each transaction, you would be able to see the address that was provided to Sage Pay.
How to see whether the customer has entered dummy information in the postcode field another way is dependent on how your integration records, interprets and translates our response to you.
Our integration requirements are detailed within our protocol guides http://www.sagepay.co.uk/support/integration-kits-protocols-document
