The way they get round that is to put all the packages for a given country, addressed but not postage-paid, in a big box. The box goes in a surface transport shipping container destined for an intermediary in that country. The intermediary takes the packages out of the box, affixes domestic postage for that country and sends them onward to the final recipient. Saves companies like Banggood or Gearbest quite a lot of money.
For small stuff that they want to ship faster, the box of addressed but not postage-paid packages goes on a plane. It costs more for the air freight, but they still save money by handling customs for one box instead of many packages, so the intermediary charges are cheaper. Air freighting a big box is also cheaper per package than sending them individually, and the intermediary can often get bulk deals for the onward domestic postal charges.
