Postfix communicating with IPFW

[Jos Chrispijn]

Dear FQ,

I recently got attacked with some dsl subscribers of this (imaginary) 
some.net domain.

These subscribers present themselves as [ip address.dynamic.some.net].
Postfix SMTP server: errors from 66-66-66-166.dynamic.some.net 
[66.66.66.166]

What I would like to do is to generate a some.net list with all these 
dynamic ip addresses and provide them to my ipfw firewall in order to 
block them on the moment that they try to relay a 2nd time thru my 
server. This will cause less process time as it is quicker to send 
someone home by the doorkeeper (ipfw) rather than check his credentials 
first (Postfix) and tell him to get lost.

Is there any way to let postfix 'communicate' with my ipfw firewall?

Jos Chrispijn