question concerning spoofing

here is the situation:

I had a user sending an email from foxnews.com to an employee within our company. Of course she used her company address to send this email. The end result being is that it got rejected. I look at this as spoofing,however the user does not understand this. How can I get around this feature of exchange rejecting emails not sent from their own domain, even though these emails are legitimate. I’ve had this problem with webex as well.

Thanks,