Re: posting a box (bulky goods)
Surface, i.e. economy, post via Swiss Post I would guess, going on our own attempts to send parcels back from the US to Switzerland some years ago. Checked the US post office price, then went to UPS and TNT who both wanted to charge $100 more just to take the package down to the post office and send it in exactly the same way! We went with the post office of course.
Swiss Post also sell a range of post boxes in various sizes so you could check with them.