Updating server extensions
The account you use will need to be a member of both the Schema Admins and Enterprise Admins security groups.For more information about how to use the Setup wizard, check out Install the Exchange 2016 Mailbox role using the Setup wizard. Prepare Active Directory domains How do you know this worked?If you have a large Active Directory deployment, or if a separate team manages Active Directory, this topic is for you. Curious about what's happening when Active Directory is being prepared for Exchange?Following the steps in this topic gives you much more control over each stage of preparation, and who can do each step. Check out What changes in Active Directory when Exchange 2016 is installed?
For example, Exchange administrators might not have the permissions needed to extend the Active Directory schema. The first step in getting your organization ready for Exchange 2016 is to extend the Active Directory schema.
Exchange stores a lot of information in Active Directory but before it can do that, it needs to add and update classes, attributes, and other items.
Updating server extensions comments