Here I am covering this topic while doing all everything such Exchange and Active Directory.
In my scenario, there is a parent domain called netoverme.info and the exchange server is installed under this domain. Then the organization is adding the child domain controller such as Management and its domain is management.netoverme.info. A Management’s domain controller is located in the site office and they just wanted to use the exchange server that was already had in parent domain netoverme.info.
When the administrator tried to create mailbox for new users that was sitting in child domain of management.netoverme.info, they encountered the problem. the UPN is not appeared as figure below:
what is the solution?
Here is the thing, we need to update the domain using the Exchange Server Installation Media and run “the setup /preparealldomains” in the exchange.
For example figure below. Make sure the preparations are fully completed.
After it is completed. Then try open the console and create mailbox for using that sitting under the finance.netoverme.info.