make outbound mail skip SA

Hello all,

Is there someway for a mailserver to scan incoming email using SA but 
not outbound?

or what I guess would be easier is to say "don't (spamassassin) scan 
email from this host" or "don't (spamassassin) scan email from this network"

Is that possible?

I have an exim mail hub that is doing incoming email for a few domains 
and outbound delivery for a few others.

Is this possible?

Thanks in advance,

- Brian