Open the message you want to reply to.
Click the Reply button in the mail window's toolbar.
Outlook creates a new message, completing the To and Subject lines. (Re: is added to the Subject line to indicate that this message is a reply.)
Outlook makes it easy to reply to a message you have received. When you reply, the recipient's address is completed, as well as the Subject line. The text of the original message is included as well. You can continue an ongoing e-mail conversation by replying to messages.
Replying to All Recipients
If the message was sent to several people and you want to reply to all the recipients, click the Reply to All button in step 2.
Type your response.
Click the Send button in the message window's toolbar. The message is sent.
Replying from the Inbox
As an alternative, you can reply to a message from the Inbox. You follow the same basic procedure as outlined here, but you select the message in the Inbox and then click the Reply button in the Outlook window's toolbar.