Restricting Incoming Email in Exchange by From Address

[Greg Jones <grjones () gmail com>]

In Exchange (any version), I would like to disallow email coming from
the Internet (smtp) that has a From address of my domain.  This would
force our employees to use OWA or Exchange (via VPN of course).  This
would help with phishing and worms that are fooling some of our
employees (e.g., emails from admin () mydomain com).  Is this possible?
 
 Greg