Detecting forwarded spam

[Michael Masse]

Is there a way for MailScanner to detect if a forwarded message has already been detected as spam by another system, therefore not needing to run it's own spam check?  

We have a large number of users who used to use a separate email provider and they now just have that email forwarded to their account here.    Their old system detects spam and creates a header entry like:
X-Spam-Report: IsSpam=yes

Right now our system just ignores that, so I was wondering if I can get our Mailscanner to take this into account and not bother with spamassassin checks if it sees this in the header?     I'm sure I could make a spamassassin rule to assign points if it saw this, but the whole point is to not have to get spamassassin involved.   

Is this possible, or should I just stick with a spamassassin rule?

Mike