Found in the string
"non-privileged users" are "normal" users, such as students.
Privileged users could be teachers, managers, admin... depending on how roles (and rights on capabilities) are defined on your site.
wonder why that expression is used, my guess is that users/students will turn into question marks when they see it.
I understand it as an attempt to use some general expression. Because it is not correct to say "teachers" - depending on the roles configuration on the site, teachers may or may not have such privilege. So "non-privileged users" means anybody who were not given explicit privilege (right, permission) to view email addresses.