Change a user’s email to an unfederated domain in Apple Business Manager
If you want users to use an email address different from that in their Microsoft Azure AD domain account, you can change it. You must make their email address and Managed Apple ID identical. An exception is that an account with a role of Administrator, Site Manager, or People Manager can’t use the same address for both.
Change a user’s email to an unfederated domain
In Apple Business Manager , sign in with an account whose role can make changes to other accounts, then tap Accounts in the sidebar.
Select the account whose email address must be changed, then tap Edit.
Change the email address, tap OK to match the Managed Apple ID, then tap Save.
Notify the user that they have a new Managed Apple ID.