Windows 2008 introduces a new kind of domain controller, the Read-Only Domain Controller, abbreviated to RODC. You can even upgrade a RODC to become a ROGC, short for Read-Only Global Catalog. Exchange 2007 (RTM or Sp1) will never use and effectively ignore any RODC or ROGC, but you can deploy RODCs and ROGCs when using Exchange 2007 (RTM or Sp1) as long as Exchange has normal, writeable domain controllers available. It may be important to note that Microsoft Office Outlook clients can use ROGCs for its Address Book lookups.
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