Why don't I pay VAT when I buy a shipping label from PostNL but I do pay VAT when I buy from you?

The law specifies that as a private individual, you do not need to pay VAT for use of the postal network and as a business customer you do. MyParcel is a corporate service provider and therefore has to charge VAT on the service and products that they offer. That VAT is specified on the invoice so that you can claim the VAT back when you are entitled to it. Only digital stamps are exempt from VAT.