Auto highlight unanswered emails

Hello all,

I work in sales and am often sending emails to leads after having initial phone calls. Now I can find myself sometimes checking what emails I have sent to which leads and can sometimes forget which leads have not yet replied.

Is there a way in desktop Outlook to automatically highlight my emails which have not yet been answered after 7 days? So it becomes very easy to precisely follow-up on the leads in a time-efficient manner.