Question : Exchange 2003 w/IMF Spoofed Spam emails?

We are running Exchange Server 2003 w/ SP2 and Intelligent Message Filter configured and enabled. Is there a way to block Spammers who are spoofing internal email addresses without the use of 3rd part spam blocker. Users are getting spam emails from themselves... Thanks for any insights.

Answer : Exchange 2003 w/IMF Spoofed Spam emails?

I haven't been able to do it, and my commercial spam blocker on the server plus another on my client will miss those too.  The thing is, it looks like email.  The spam score is not high enough to make it fall into the spam folder, so we live with it.  I'm really unsure why they do this, as it seems to have no value to anybody.