Before you move mailboxes you need to make sure the BESAdmin account has the appropriate permissions on the new server:
KB02276 - Assigning permissions for a BlackBerry Enterprise Server service account
After you move the mailboxes you should perform a handheldcleanup:
KB00140 - Run handheldcleanup.exe
Are you also moving the BESAdmin mailbox?:
KB03296 - How to move the BlackBerry service account mailbox
Other than the information in the KB articles there are no configuration changes that need to be made.