You can move your Besadmin account from Exchange 2003 to Exchange 2007 any time during the migration. Only thing is that you need to make sure that BESadmin account has sufficient rights on Exchange 2007 store before you migrate to Exchange 2007
1. Stop all the services blackberry service starting Blackberry Router, Blackberry controller, Blackberry dispatcher and followed by others
2. Move the account to the new server
3. Remove Microsoft Exchange System Manager 2000 or 2003. (A Microsoft Exchange Server installation CD is required to complete this step.)
4. Perform a search for MAPI32.dll and cdo.dll
5. Rename any cdo.dll and MAPI32.dll files from the system32 folder and the program files\exchsrvr\bin folder to a .bak file extension
6. Download ExcchangeMAPICdo.exe and install, see KB12697
7. Edit MAPI profile and type the new maibox server name Restart the services in order Router, Controller , Dispatcher and followed by others
8. If above steps did not work then follow the below instructions
9. Stop all the services again then open Registry go to HKEY_CURRENT_USER\Software\Microsoft\Windows NT\Current Version\Windows Messaging Subsystem then Right click on the folder Profiles and export it for the backup and delete the same
10. Open Blackberry Server configuration, on blackberry server tab click on Edit MAPI profile and enter the new server name for the besadmin.
11. Open Edit MAPI Profile and again input the new server name of the besadmin and configure the same.
12. Start all the blackberry service.