Domain validation Office 365 and AAD

Question

I have set up a directory synchronization between Azure and my Active Directory, have validated my custom domains and now I would like to setup a hybrid Exchange migration to Office 365. I have a separate account to manage Office 365.

One of the prerequisites is a domain validation in Office 365. Doing so result in an error since my domains are already validated in Azure.

Should I move all my resources to the Office 365 directory ? This seems not possible, so I guess I would have to restart the setup (App Services, SQL DB...) from the beginning ?

I guess I don't do this in the right way. Could someone light my way ?

Thank you.

EDIT : Office 365 is used by a very small percentage of my users for now (which are new users), 20 on ~3500. The others are still working with Exchange 2013. I would like to plan a migration in batch.

Answer 1

as I understand the question the problem is that you have two Azure AD tenants one managing your AZURE subscription and on managing you O365 subscription. it is correct that a custom domain can only be registered against a single Azure AD tenant.

The solution is to add the o365 Azure AD Tenant to you Azure subscription and make it the managing directory. this link https://docs.microsoft.com/en-us/azure/billing/billing-add-office-365-tenant-to-azure-subscription

will show you how to make your O365 directory appear in azure and how to make it the management directory for your Azure subscription.

once this is done the same sets of users and groups will be available in both office 365 and azure and you will be able to sue the same custom domain in each.