Postfix restricting local mail locally.

[Kendrick]

I am trying to make it so that postfix takes specific actions when spam 
"from" my domian externally arrives.  smtpd_recipient_restrictions / 
reject_unknown_... looked prommising but I dont see how to work it with 
the information given.

When a new message arrives with [from: somt...@mydomain.com] 
[to:somt...@mydomain.com] and sender ip address does not = $mynetworks i 
want to send connecting pc's ip to external scripts if possible and the 
least reject the message.

reverse dns lookup from my internal dns server would work as well. 
eventually I may be interested in having tls or something authenticate 
external users to send from mydomian but that is not a big concern right 
now.  If need be vpn will solve that need.

any suggestions are appriciated. If I missed a how-to or something I 
appriciate the links.  I dont always figure the best key words to find 
these things.

Kendrick