One of my biggest gripes about Exchange 2003's Intelligent Message Filter was the inability to filter our own internal email senders' email. I found this article that explains how to let IMF check on authenticated sessions. I believe if I do this on the bridgehead server for my org, it will only filter things that leave the organization and will let our internal "spam" continue.

To do this find HKLM\Software\Microsoft\Exchange\ContentFilter in your registry. Add a new DWORD value of CheckAuthSessions and set it to 1.

I'll update this post if there are some unintended consequences to this action.