Posting fragile and delicate packages across Australia has never been simpler or safer, but if you're posting perishable food items you may run into difficulties. Without a little care and research, it is easy to fall foul of the stringent laws regarding transit of perishable foods and receive the dreaded notice of non-delivery, and even perfectly packed foodstuffs can turn into a stinking mess during transportation. This should not discourage you from sending perishable foods by mail, however, as choosing the right packaging can make the whole process much smoother.
What are the regulations for sending perishable foods by mail?
What you are and aren't allowed to send in the post will depend largely on where in Australia you live, and where you intend to deliver to. Various interstate postal restrictions designed to avoid ecological contamination mean that some foods (particularly fruits and vegetables) will not be allowed across state lines. If you are delivering to a different state, check the postal restrictions in place in both your state and your package's destination.
If you are sending food within state lines, restrictions are not so stringent. As long as a foodstuff is packaged well enough not to leak any fluids, and the food does not become noticeably rotten and smelly during transit, you should have no problems. Just make sure to choose a delivery service quick enough to deliver your food before it turns foul. A full guide to postal restrictions enforced by Australia Post can be found here.
Obviously, the food itself should be packed in a container that is as airtight as possible, and must be packed in a watertight container at the very least. Sealed plastic bags and containers are ideal, although plastic containers should ideally have double locking to avoid a bad knock making a huge mess.
Whatever you put the food itself in, it should be suitably padded. Paper packing materials such as old newspapers don't really provide enough cushioning, so you should opt for a more heavily padded material. Bubble wrap and air cushions are good choices, as are polystyrene packing peanuts and solid polystyrene blocks. Solid polystyrene is also an excellent heat insulator, and will protect heat-sensitive foods from external sources of heat and cold.
As for the outer box, anything sturdy enough to avoid being easily crushed will do. Padded envelopes are generally not sufficient unless your package is being delivered individually by courier -- timber or cardboard packing crates are better. If using cardboard boxes, make sure to use a new one, as cardboard boxes quickly wear out and lose structural strength with use. You may also want to line the interior of the outer box with a watertight plastic or rubber liner if your foodstuffs are capable of spilling. Make sure the box is clearly marked as fragile, and has any stickers or stamps signifying perishable contents that may be required.
If the food you are sending requires chilling, or it will last significantly longer if the package is chilled, you might wish to insert a couple of frozen gel packs to keep the interior of your box cool. If you really want to make sure your food doesn't spoil, polystyrene containers containing dry ice may also be useful to you, but this is generally only be a viable option if you are delivering by courier. Make sure that the delivery company and the relevant delivery personnel know when a package contains dry ice, as it can be a dangerous material to an unwitting delivery worker and can cause skin damage if spilt.