Restore Prerequisites

Before you can restore document level backups, you must satisfy the following prerequisites:

The Exchange server must be running and the storage groups and mailbox stores that you are restoring to must already exist (they are not created at restore time), and the mailbox store must be mounted.
The account you are using to restore must meet the backup agent service account requirements for the machine you are restoring to. For information on these requirements, see Backup Agent Service Account Requirements for Document Level Backup and Restore.

More information: