Identity and Access Management, Student seeking readmission/re-entry
This is not necessary; in fact processes state that the Student's netid will only be reactivated after they've been approved for reentry/readmission. (see: https://grad.illinois.edu/gradmap/quick-guide-reentry)
If you are a grad student, you need to go to this page:
https://choose.illinois.edu/portal/petition_apps, and choose the 'first time user' link.
You are a first-time user of this reentry petition portal, thus need to request an account for that purpose. You can use any email address to create this account.
If you are undergrad, your school may have its own page (ex: https://forms.illinois.edu/sec/3507139 for Grainger, https://apps.atlas.illinois.edu/FormBuilderSurvey/Survey/las_administration/student_academic_affairs/las_re_entry_application_process/ for LAS) to petition for readmission or re-entry.
You will need to look up your school's policies and procedures for reentry/readmission or contact your college for instructions.
No one will need their netid or Exchange email reactivated to do so; reactivation happens automatically AFTER their petition has been accepted and approved, not before.