Reminders in Outlook are usually associated with the Calendar but you can also add reminders to messages. For instance, you may want to follow up on something in an email a few weeks or months in the future. You can create a reminder for any message you have sent or received.
To add a reminder to an email:
- Right-click on the message, select Follow Up, Add Reminder

- In the Custom dialog box, below Reminder, select the date and time for the reminder

- Click on OK
Note that the reminder time defaults to 4p.m. so you will typically want to change it to earlier in the day.
Any questions, please let me know.