Please review the "Configuring Outlook 2010" document to find the location of the "Advanced" within the "Internet E-mail Settings" window if you are not familiar with configuring Outlook.
At the bottom of the Advanced tab you will see the "Delivery" section. you should check the "Leave a copy of messages on the server" box and then check the following 2 boxes if desired. I usually recommend leaving mail on the server for 10 to 15 days but this can be set to a higher or lower number based on personal preference.
