How do I know if I set the reminder correctly?

When you set a reminder, the ‘Remind Me’ button becomes checked and its color turns to orange to indicate that it is in active state. Also it appears at the bottom of the window after you set a reminder successfully. Likewise, if you check back that email or conversation which you have set a reminder before, the ‘Remind Me’ button is again indicated in orange-colored active state. Furthermore, when you hover over the orange button with your mouse cursor, you can see a tooltip that indicates the reminder date.