Proxying a policy service

[Adrian Overbury]

Has anyone ever written a proxy server for policy services?  I have a 
policy server (grossd, one of the best greylisting engines I've ever 
used) that, if it goes down, causes my Postfix servers to temp fail 
everything with 'Server configuration problem'.  This is a real problem 
for me.  I'd like to proxy the service so that, if it goes down, the 
proxy responds with DUNNO and the message continues to be checked 
against the next item in the chain.  Does anyone know of anything 
pre-made that can achieve this, or am I going to have to write it myself?

Adrian