You have Exchange 2013 CU9 running in your environment and you want to configure the option to store sent messages in the shared Mailbox instead of the user’s mailbox as described in my blogpost Exchange 2013, Shared Mailbox and Sent Items.

But when you open the Exchange Management Shell and try to change the Mailbox settings using the Set-Mailbox cmdlet, the options -MessageCopyForSentAsEnabled and -MessageCopyForSendOnBehalfEnabled are not available.

To solve this you can run the setup.exe /PrepareAD /IAcceptExchangeServerLicenseTerms command from the CU9 installation media.

But why wasn’t this run during installation of Exchange 2013 CU9 in the first place?

You might expect that when running the setup application (either using the GUI or using setup.exe /mode:upgrade) that the upgrade of the Active Directory Configuration partition automatically takes place.

However, this is not always the case. It turns out that when there are no Schema changes during the upgrade process, which is the case when upgrading from Exchange 2013 CU7 or CU8 to Exchange 2013 CU9, the preparation of the Configuration Partition in Active Directory is automatically skipped by the setup application.

This is a bit annoying and nothing will break (except the fact you’re missing some new functionality) and can be solved by running the Setup.exe /PrepareAD later on.