What is it you need to back up? Are these Exchange accounts or ISP mailboxes or some other mail system? Please specify. Are these POP3 accounts and you need to back up the pst’s? Please provide more information. If you have a product backing up the local drive then the pst file is already being backed up. Outlook Per Se does not need to be backed up, it can be re-installed, so we really need to know what exactly it is you are needing.Thanks.
Symantec Backup Exec is a good backup application thats worth looking into.
If you are looking to backup client PST files, a start would be the PFBackup utility from Microsoft. Now this is not an enterprise level tool but can give you a good start in keeping a backup copy of local user PST files.
Outlook 2007/2003/2002 Add-in: Personal Folders Backup.
The Personal Folders Backup download creates backup copies of your .PST files at regular intervals, in Outlook 2002 and later versions, making it easy to keep all of your Outlook folders safely backed up.