To 'properly' open any email you need to double-click on the header. So I'm guessing that what you're referring to is the content of an email appearing in the preview pane when you delete the previous email (or move it to another folder).
The simple answer is to get rid of the preview pane. As well as helping you achieve what you're seeking to do, it will also make your PC more secure. (Some malicious programs can be initiated simply by opening the email which they're attached to. That includes viewing them in the preview pane. If you get rid of that pane you'll be able to delete any suspicious mail without opening it first).
You can disable the preview pane by going to View>Layout, clicking to remove the relevant tick, then clicking 'Apply' and 'OK'.
Chris