exchange server 2000 and outlook 2k3 - HELP

[ubergeek7]

there is an exchange server in place that distributes a global list of e-mails and distribution lists. problem: when upgrading to outlook 2003 we hit a snag. if a e-mail comes in from the outside (yahoo for example) and one is to forward or cc the mail on a dist list, then it fails because it tries to route the mail straight to the internet instead of to the exchange server. you can click accounts tab and select exchange but everyone would have to do this everytime they e-mailed. can anyone help?

Thanks for your Time!