Question about Outlook Express

I have the default installation of Outlook for MAC 2011 (14.3.7 - 130812).  I have setup an Exchange account for my work and two POP/iMAP accounts for personal use.  I am trying to understand the folder structure for the email (and any attachments to the email) for each account.  What I am trying to do is exclude backing up the directories that contain any messages/attachments associated with the Exchange account since that is already backed up at the office.  Therefore, I would only be backing up the email and attachments associated with the two personal accounts.  The work Exchange account is very large and since I am paying for backup capacity on my laptop, I don't want to pay for the large amount of work email to be backed up!