Thank you for your answer @Patrick.
For taxes, you mean that if the end customer is an individual, say in the US, he would not have to pay US local tax on the product? (So that's what I need to check?)
For the customs, we send ourselves and go through the post office, so is it also question of package? Knowing that no shipment will exceed € 50 in value, do you think we will be duty-free in just about every country (European Union, North America)?