When you configure an Outlook profile to use Cached Mode the client software uses a special address book to resolve email addresses and other information. This address book is named Offline Address Book (OAB) and is built and provided by the Exchange Organisation hosting the mailbox. The client downloads OAB changes when Outlook starts and checks for further OAB changes in intervals.
OAB provides address resolver capabilities when there is no network connection to Exchange Server or a domain controller available. In addition to resolver capabilities, the OAB contains other important information, e.g., send-as permissions and information regarding public folders.
For security reasons it might be necessary to disallow the download of the Offline Address Book by an Outlook Client. In this case, you control the download functionality with the Windows System Registry. You can disable the OAB download using the following registry key:
OutlookCached ModeValue type: REG_DWORDValue name: DownloadOABValue: 0 to not download the OAB
With a deactivated OAB download name resolution in Outlook Cached Mode requires network access to an Exchange Server
Enjoy Exchange Server.