Use e-mail address as “Work or School” account?

[ThomasEngine]

Exactly what makes an email address recognized as a work or school account?

Does the email address need to associated with an Office 365 commercial license or would syncing a local domain account into a free Azure AD tenant automatically convert the email address into a Work or School account? If so, is it the SMTP address or the UPN that’s actually recognized as Work or School as opposed to personal MSA?

If an email address is able to be used as a work or school account, does the user still have the option to also use that email address as a personal MSA if they choose to?https://9apps.ooo/