[Leica] Palo Alto Control, we have a possible solution and an alternative

[hartzell at alerce.com (George Hartzell)]

I've had huge success lowering the load on my postfix based
mailservers with greylisting, it really reduces the amount of stuff
that gets passed through to spamassassin et al.

  http://www.greylisting.org/

Once in a blue moon I have to manually whitelist some system that I
care about but that doesn't follow the RFC's but it's never been a
problem in real life and I doubt that would come in to play much with
mailing list addresses.

g.