Exchange 2003 mailbox may not be seen in the restore view from a successful Granular Recovery Technology (GRT) enabled backup set on tape.
Granular Recovery Technology (GRT) backup of Exchange 2003 on tape does not show mailbox if:
A. Mailbox contains an underscore i.e. "_" in its alias name. This issue will come up only for those mailboxes where alias name is changed later to add "_" . This issue may not be seen for users which were initially created with "_" in the alias name as they will also have "_" in the name.
B. Mailbox has dissimilar values for the attributes LegacyExchangeDN and mailNickName
This issue is resolved by Backup Exec 2010 R2 Hotfix 143746
Duplicate the backup set from tape to disk. The backup set on disk will show all the mailboxes restore selections.
Use Recovery Storage Group to restore contents of mailbox(s).