Get icon badge for mail reminders

It looks like I should be able to set an email to remind me later and receive a badge on the mail app when the reminder goes off. This doesn’t happen though. I have to leave the email unread but then the badge shows all day.

Can somehow explain how this SHOULD work? Should I be able to read the email, set a reminder on it, and have the app icon badge display when it is time? Should the email also show unread in my inbox?