on 07-06-2015 12:39 PM
Some sellers use pre-paid large letter envelopes. You can post them in a red street box. No need to go to the PO.
You do have to watch that the envelope is no more than 20mm thick, and less than 500g weight. They are supposed to be for documents only. But if you are posting something else you might want to enclose the item between 2 pieces of thin cardboard to help disguise the contents. Providing you don't exceed the weight and thickness requirement you should be ok.
A handy thing to have is a letter gauge. A sheet of cardboard with 20mm and 5 mm slots to pass your letter through and make sure they're ok. You used to be able to get them for free at the PO.