Add 2 layouts in a wrapper section. First layout should embed a section with 4 tabs and the next will embed another section with only the drop down(Even you may add the drop down directly in the 2nd lay out).
You may use column lay out for this. In your wrapper/mail section add a layout. While dragging it, select column layout with the second option that is Main then side as shown in my attachment. Then on the main column drag a section with your tabs. On the side column at the right, add your drop down.