A "mail order" company ships merchandise bought and paid for over distances. Amazon.com, Ebay, sell things this way. They do NOT do the 'delivery' part and so are not 'letter delivery' companies such as DHL or UPS. The mail order company takes the order for the merchandise, packs it up, and then hands it off to a company like UPS or DHL or a postal service to deliver it - after the mail order company has first packaged it. The mail order company is not responsible for delivering it and the delivery company is not responsible for how the item was packaged. In this way, if the item arrives damaged, they can both blame each other, unless you paid extra for shipping insurance.
Filling all the spaces:
Example: a fragile piece of glassware, perhaps a vase about 3 inches in diameter, and 8 inches tall, shipped in a carton (which is a cardboard box), where the carton might be rectilinear (all sides rectangles or square) which might measure 8" by 8 " by 12". If you simply put the vase in the box and ship it, the vase will be tumbled around in the box during shipping and get broken against the insides of the box. If the vase is wrapped in bubble wrap in such a way that it has at least 2 inches or more of padding on any side and packed so that it can NOT shift around inside the carton (box), then it should arrive undamaged, unless the box got seriously squashed into dimensions smaller than the vase. In most cases, if you don't pack something well enough to survive a 5 foot drop onto concrete, it stands a good chance of arriving with damage. "Filling all empty space" must be done with padding materials and provide sufficient distance between the object and the side of the box. A relative once shipped me a large carton of glass dinner dishes, bowls and heavy glasses and all the empty space was filled - with the glassware. He had added NO padding, not even crumpled newspapers or paper towels between the plates in the stack. He shipped about 40 pieces of glassware. About 500-1000 pieces were found in the carton when it was opened. One bowl and two of the heavier glasses somehow survived - probably using the crushed remains of the other glassware as 'padding' - LOL! Oh well, we didn't have kitchen space for all the other plates anyway.