If you use Veritas Backup Exec, in order to be able to restore individual mailboxes, you would have had to include in you backup job the following three items of your Exchange server: Microsoft Exchange Directory, Microsoft Exchange Information Store, and Microsoft Exchange Mailboxes. You should not have backed-up any of the \exchsrvr folder on any drives, otherwise the is a slight possibility of database corruption. These folders should only be backed-up if you are performing a static database backup where all Exchange services are stopped. But this will not allow you to restore mailboxes individually.
Then to restore an individual mailbox, it is as simple as defining a Restore job and selecting the mailbox to restore by drilling down the file tree on the Backup server that is running Veritas to:
<backup server name> -> Remote Selections -> Microsoft Windows Network -> <domain name> -> <Exchange server name> -> Microsoft Exchange Directory. Also select Exchange Information Store and Microsoft Exchange Mailboxes.
Save your job definition and then run it.
This assumes that your Exchange server is a different server than your backup server.