If you ever write Microsoft Outlook messages for someone else (say, weekly team reports for a manager to review and then send), just write the message normally. But be sure to only save it (don't send it), and a copy will appear in your Drafts folder.
Drag your finished draft into a new message addressed to your boss so it's added as an attachment.
Now here's the trick. If your boss opens the mail and tries to send it, the Send button will be grayed out. Be sure to let your designated senders know that your attached messages must be dragged into their Drafts mail folders to enable editing and sending.