Consider the following scenario. You add the showInAddressBook attribute manually to a Microsoft Exchange Server 2007 mailbox. You do this so that the mailbox can show in certain address lists. You run certain commands on the mailbox, such as the Set-Mailbox command, or the Move-Mailbox command. In this scenario, the mailbox is not shown in the address lists.
This issue occurs because the address lists entries are removed incorrectly from the showInAddressBook attribute in the Active Directory directory service.
To resolve this issue, install the following update rollup:
2509911 Description of Update Rollup 4 for Exchange Server 2007 Service Pack 3
After you apply this update, create the following registry subkey on the Exchange Server 2007 server: