The Australia Post Barcode Sort Plan (BSP) number enables letters to be pre-sorted by area prior to sending. This saves Australia Post time and effort as the mail is already correctly sorted. They pass this saving onto you by giving you further mail discounts. The BSP numbers currently range from 1 to 54.
The merge field for the BSP is called BSPNUMBER. This field should be Arial font, size 5.
When creating the mailing, ensure that the mailing is sorted by BSP number.