When you receive a message, you can reply directly back to the sender. You also have the option of forwarding the message or sending a response to everyone who receives the message. When you reply to a message, Outlook keeps the original message text and lets you add your new text above the original text. The sender’s name becomes the recipient name, and the subject line begins with "RE:" to denote that the message is a reply.
Click the Inbox icon on the Navigation Pane to display messages in your Inbox folder.
Click the message to which you want to reply.
Click Reply on the Standard toolbar. ...