Would it be suffice with an .edu email, or does one need a formal document from university officials? I tried to click through from the sandbox link, but a Yahoo account is required.
Most places only care that you were a student with active edu. I graduated years ago and I still use the edu without problem. Most things say you need to be a student from university. Which I am/was. Very few places say actively enrolled student. It's a legal gray area in my opinion.
Many schools will give alumni edu addresses as well
Do you mean to technically get access, or to be legally allowed to use it ? Because for the latter, merely having a .edu isn't enough.
It's probably more complicated than that, because I assume there are places in the world where you can legally ignore someone trying to enforce such claim where they are outside of such jurisdiction.
I have a lifelong edu address but it's not what they mean of course. My reading is that you have to be an enrolled student or researcher.