Australia has a postal system which is reasonably efficient. One oddity of the system is that G.S.T. (Goods and Services Tax) applies to domestic postage, but not to international postage. As a result, different stamps must be used for the two purposes. When purchasing stamps, therefore, you must make it clear whether you require domestic stamps, with G.S.T. included, or international stamps, on which G.S.T. is not paid.
For items weighing up to 250 grams, a prepaid air mail envelope can be purchased. If you buy a pack of ten such envelopes, the cost of the envelopes themselves is negligible. You pay only for the postage. If your envelope weighs more than 250 grams, you may add the extra postage.
The Poste Restante system allows mail to be held for you for collection at any post office for up to a month. There is no charge. At the larger post offices a computerised system is employed and you can use a computer terminal to check whether you have mail or not.