It's easy to create an appointment from an email in Microsoft Outlook: just drag the email message to the calendar and drop it.
You can drag an email to one of the buttons on the navigation bar then drop it to create an appointment with the contents of the message in your default Calendar or you can hover over the button to expand the navigation pane, then drop it on another Calendar.
Right-click (or hold Ctrl) and drag to see the menu with additional options.
If you prefer not to drag the message or it's open in a new window, you can use the Move to (or Copy to) Folder command to create a new appointment.
This works with any Outlook folder and in all versions of Outlook (desktop versions).
Outlook 2016 and insert as a Shortcut
A change in Outlook 2016 to support HTML in appointment bodies affected the ability to create appointments with shortcuts, as the shortcut is inserted an linked object, which is not supported by HTML formatting.
The user can either change the appointment format to Rich Text to show the shortcut or change the default to Rich Text. If you want to change the default to RTF, see this article for the necessary registry key:
"Create an Outlook Appointment from a Message" (uses entire message body)
"Create Task or Appointment and Insert Selected Text" (pasts selected text into appointment or task body)