By using a rule that you create, Outlook can examine each message that you receive for certain characteristics and then automatically forward or redirect any message that matches the characteristics to another e-mail account.
There are a couple of ways of doing it: forwarding and redirecting.
When a rule automatically forwards a message you receive, it leaves a copy of the message in your Inbox or in the folder to which the message was originally delivered. The rule then adds the designation "FW:" to the beginning of the Subject line, changes the message formatting, and then forwards the message to the account specified by the rule. The recipient represented by the account also sees that the message came from you.
When a rule automatically redirects a message you receive, it also leaves a copy in your Inbox or in the folder to which the message was originally delivered. The rule then sends the message, unchanged, to the account specified by the rule. To the recipient, the message appears as though it came directly from the original sender. There is no indication that the message was delivered by way of your account.