You are preparing to upgrade from an Exchange Server 2003 environment to an Exchange Server 2007 environment. You need to ensure that internal users and remote users are able to access their mailboxes during the transition from Exchange Server 2003 to Exchange Server 2007. What should you do?

A.
Install the Exchange 2007 Client Access server role.

B.
Install the Exchange 2007 Hub Transport server role.

C.
Install the Exchange 2007 Mailbox server role.

D.
Install an Exchange 2003 front-end server.