A friend told me what to do: Go to the "TOOLS" menu item (ie., File, Edit, View, TOOLS...) then select 'Accounts' from the drop down menu. It should bring up a new window in which there will be various email accounts to select from. Perhaps only one. Select the one you use and click the "properties" button on the right. This will bring up another window with various tabs. The one you want to click is "advanced". At the bottom there is an option to leave messages on the server for so many days. Do this same config for both of your computers.
Well I did and it works just fine now!