we allow customers and guest users to create accounts in our identity system using their corporate or personal emails.
If I use AD Connect to sync those user accounts, as the email address of customer accounts wont be one of the registered domain names in the tenant, their UPN will change to firstname.lastname@example.org which is not acceptable.
Is there a way to migrate those accounts to Azure AD while allowing the users to keep their current usernames and passwords to have minimum experience change for them?
How do other organizations handle/handled such migration which I am pretty sure should be very common scenario.
Is B2C only the option here?