View federated-authentication user name conflicts in Apple Business Manager
After a domain is successfully added, Apple reviews all existing Apple IDs by searching for any using that specific domain name. If an Apple ID is found to be using the domain name, Apple Business Manager lets you send a mail message—and a notification to any device connected to their iCloud account—to that person, letting them know they must update their Apple ID username so that you can use it for your organisation. During the update process, they do not have to change their password and all their purchases and data remain in their account.
For example, say your organisation registered the domain @acme.com several years ago and set up email addresses for all their employees. Jane Appleseed decided to use the email address she was assigned 'email@example.com' as her personal Apple ID.
Even if Jane no longer works for the organisation that registered acme.com, she still has the Apple ID with that domain name. Because you are setting up federated authentication for the domain name @acme.com, Jane must change her Apple ID username so you can create the Managed Apple ID firstname.lastname@example.org if you want.
View federated-authentication user name conflicts
In Apple Business Manager , sign in with an account that has the role of Administrator or People Manager.
Click Activity in the sidebar, then click Checking for Conflicts.
If any username conflicts are found, you will see a dialogue with the total number of username conflicts.
Click Continue, click Send Notifications, then click OK.
A mail message is sent to each user with a username conflict, as well as a notification to any device connected to their iCloud account, letting them know they must change their personal Apple ID.
You can view the process of sending mail messages to users with a username conflict in the Activity section of Apple Business Manager.
How Apple notifies users whose Apple IDs conflict
Apple will identify users whose Apple ID contains the domain name you have registered. Those users receive a mail message and a notification telling them they must rename their Apple ID. If they have not renamed their Apple ID yet, they keep receiving notifications and mail messages, with one final mail message at 60 days. After 60 days, the user’s Apple ID is automatically renamed to a temporary user name, and the original user name is released and claimed by your organisation.