The Portuguese Post Office has a product called "Correio Verde" (green mail).
This is a product where you have ready-to-send packages, with no need for weighing or stamps.
As long as it fits in the package, any thing can be send. It's Ready to Go.
The Target is urban people, liberal professionals and companies, in an active age, between 23 and 65.
It is simple.
No weight, no stamps.
Always ready to send.