Exchange Server Anti Spam Software How Can You Stop Email Spoofing On A Network?

How can you stop email spoofing on a network? - exchange server anti spam software

I'm running Exchange Server 2007 with the anti-spam protection. I also run your email through a Barracuda. I still get through fake e-mails (e-mails that say that the sender address is the same as the receiver). Barracuda has helped little. Has anyone found another way to stop them?