Backing up emails

Hi

I have a network running Windows 2000 and on the server I use Veritas BackupExec 9.0 to backup everything. Once a week I alter the backup selection to backup just the emails on the network. The emails for all my staff are handled by Exchange 2000. My question is in the backup selection do I select "Microsoft Information Store" or do I have to select "Microsoft Exchange Mailboxes" in order to backup all email accounts and emails? What is the difference? I have so far been backing up just the "Microsoft Information Store" assuming this includes all the mailboxes (is this true?), and this backup has always completed successfully.

Last week I thought I would try to backup just the "Exchange Mailboxes" but the backup failed, which I assume was due to Veritas attempting to backup something that was currently running, i.e Exchange. Anyway please can anyone confirm if just backing up "Microsoft Information Store" is all I need to do to have a full back up of all our emails.

Thank you for any help and information.

Matt