 To mark special occasions, Australia Post occasionally releases unique and limited-time only postal stamp designs, and less frequently, specially designed postal products.Before the formation of Commonwealth of Australia on 1 January 1901, each state of Australia issued separate postage stamps through colonial mail systems.After the federation in 1901, the mail systems merged and formed the Postmaster-General's Department (PMG), whose responsibilities included the provision of postal and telegraphic services throughout Australia.