Log onto your email account and make sure you are using the "right" preview view. You can do that by clicking on the "change view" at the right hand side.
Once there go to the search box at the top of the email list and click on the icon to the right that looks like a funnel. This will open a box where you can set the emails to be listed in various ways, one of which is by unread emails. Click on that and it will list all your unread emails first.
Once you have done that you can change to your preferred view and the setting will be retained.
