How does one enter a timestamp into the message part of an outlook email?
It’s Email, you don’t need a stamp!
The message is automatically timestamped when sent, whether you like it or not.
If you’re just trying to paste the current time somewhere into the body text of the message, well that depends.
Outlook normally is configured to use Word for the editor, so the same keystrokes or menu commands that will paste the current time into a DOC will work in Outlook too. But depending on which version of Outlook, or Outlook Express or … you have and how it’s configured, you may not be using Word as your editor. And the editor you are using may have a different, or no, command for inserting the current date & time.