Hi @agutschow ,
But we using Azure AD as read only purpose means we are not doing any provisioning as AD and AAD is in sync. But customer came up with DL assignment which is from AAD. For Manage Exchange Online we required IQService and other things.
Kindly note that to Exchange Online Management you must required IQService and need to create user in Microsoft Entra ID with the Exchange Administrator role.
Please refer below link for configuring the same.