multiple mailscanners with milter-null

[Mike Masse]

I've seen Julian's suggestion to use Milter-null to combat backscatter 
and like the idea, but am curious anyone knows if it's possible to work 
with different outgoing and incoming servers?   I have 3 MailScanner 
servers in front of my message store servers.   One of the MS machines 
is for outgoing, and the other two handle incoming with MX based load 
balancing.   If the outgoing puts a hash in the header of the outgoing 
messages, will the incoming server's recognize the outgoing server's 
hashes?

Mike