Thanks for your reply.
1. In the volumes i can see : the server name, with its hard drives, and below the hard drives, the "Exchange Server" subtree with its two storage groupes (as configured in Exchange), and below, the "Exchange Mailboxes" subtree with all mailboxes inside.
2. In the log it says:
Resolved container "Exchange Mailboxes" on ORCSIPEXCHPROD1 to 59 volumes:
etc.
etc.
To Backup Set "Exchange"
07/11/2008 22:01:45: Copying Adm-sauvegarde on ORCSIPEXCHPROD1
07/11/2008 22:02:30: Snapshot Stored, 10KB
07/11/2008 22:02:43: Execution completed successfully
Completed: 10 files, zero KB
Performance: 0,0 MB/minute
Duration: 00:00:57 (00:00:41 idel/loading/preparing)
and so on for each mailboxe scanned. Adm-sauvegarde is the RBU user. Other users have some mails backed up and so the number of files and KB and performance is not 0.
3. In "Reports" ==> "Database Backup History", it says : No known databases.