This option is appropriate for short-term forwarding of e-mails:
Open an OWA session (preferably with Internet Explorer) and click the button at the bottom which says 'go to rules' when your cursor is over it. In the Edit Rule window press the New button; give it a meaningful name; at the bottom of the window select 'Forward it to' and fill in your offsite email address in the field at the right. Decide whether you want a copy kept in your Exchange Inbox and check or uncheck the box just under your offsite email address accordingly. Press Save and Close button. You'll get a prompt warning you that this will affect all messages you receive. Just press OK to acknowledge this.
Anyone needing long-term forwarding (several months) should request the change be made by the mail-admin team as described here: http://www2.slac.stanford.edu/comp/messaging/using/forw_exch.htm. Due to the overhead in this configuration we request that you only choose this when your forwarding is going to be for several months, and only for ACTIVE employees and users.