All you need to have is a way of proving your anteriority if anyone were to come and claim they’ve written it instead of you.
A modern alternative to sending a sealed package is digital watermarking.
Francesco, as you are italian, you may want to try this "almost free" service:
https://www.costozero.org/wai/copyzero.html https://www.costozero.org/wai/u2.html or buy a smart card to do it yourself
