 There are exceptions; the major town of Ipswich, Queensland has the postcode 4305, while Goodna, a relatively unimportant suburb of Ipswich, is allocated 4300.Australia Post prefers envelopes sold in Australia to have four boxes in the bottom right corner of the front of the envelope.Entering the postcode in these boxes or squares, which Australia Post calls "postcode squares", enables Australia Post to use optical character recognition software in its mail sorting machines to automatically and more quickly sort mail into postcodes, which also embeds routing information.