I have previously used the following method to forward messages to an external account:
First, I create a mail contact in Exchange with the e-mail address being that of the external account. I then create a rule in the local account for all messages received to be forwarded to the mail contact(external account). This method gets the job done, but i'm curious if any of you have a better (easier) way of doing this.
FYI, the reason i'm forwarding messages to external accounts is because the executives don't like having to check more than one account for e-mail.