If you have a domain, DO NOT follow links like "register a pec" or "pec" or something that is similar to the right choice.
If you have a domain:
- login in your customer area;
- go to your domain and click on control panel;
- once there, go to email service -> show all;
- scroll down, you'll see a box "PEC on domain";
- follow the purchase procedure from there.
The wise man said: if it seems the right choice is always the wrong choice, obviously only if you are on Aruba.