sendmail access control

[Justin Zygmont]

I was wondering if anyone that knows sendmail well enough to say if 
something like this can work?

/etc/mail/access

192.168.0.1		RELAY
192.168.0.2		RELAY
192.168.0.0/24		REJECT

as it implies, I want to allow only certain hosts to send outgoing email, 
while rejecting all others, even if authentication is used.  However 
internal email should still be allowed.

Is there a way to do it?

Thanks, Justin