In an existing environment you need to do the following:
1. Install & setup exchange 2007
2. Migrate users to your Exchange 2007 server
3. Ensure you are running BES 4.1.3 or higher
4. From the Exchange 2007 server open the “Exchange Management Shell” which can be found in the Exchange program group. From EMS run the following two scripts to set the delegate control and required permissions:
get-mailboxserver <mail_server_name> | add-exchangeadministrator BESAdmin –role ViewOnlyAdmin
get-mailboxserver <mail_server_name> | add-adpermission –user BESAdmin –accessrights ExtendedRight –extendedrights Send-As, Receive-As, ms-Exch-Store-Admin
5. Stop all the Blackberry services and remove ESM for Exchange 2003 from your BES server. Or unregister mapi32.dll and cdo.dll if the files had just been registered manually without installing ESM.
6. Download and install Microsoft Exchange Server MAPI Client and Collaboration Data Objects 1.2.1 on your BES server.
7. Restart your BES server.