Simply drag and drop the message from Mail to the Reminders application icon in the Dock. The Reminders app will present a new item in your default list with the name of the email as the title, and a link to the message. Clicking the link will open the email in Mail. You can easily set a reminder for a location or date, along with a priority from here.
You can also drag and drop an email from the Mail app into the Calendar app on a specific date. This will create a new event on that date.
If you've ever wished you could schedule the opening of a specific file, or set an application to launch on a specific date and time, either on a one off basis or on a recurring scheduled event, you can actually do both right in macOS with the help of none other than the default Calendar app.
• Open Calendar in macOS and create a new event, either by clicking the [+] plus button or by double-clicking on any date
• Double-click the event to display event details
• Click on the date and time section
• Pull down the "alert" menu and choose "Custom…"
• Pull down the "Message" menu and choose "Open file"
• Directly under the menu, pull down the next menu and choose "Other...", then use the file browser to select the file you want to open on a schedule
• Choose "OK" when finished
Once the date arrives, the selected file will launch automatically in the default application at the date and time specified in Calendar as the alert. Use the “repeat" function to set the file to consistently relaunch on the given date and time provided. These can be standard, or custom repeating schedules like every last Friday of the month. The repeat feature is an excellent additional trick for repetitive tasks that use the same file, like a weekly or monthly earnings report, tax document, expense sheet, or whatever else requires regular use on a scheduled basis.