My exchange server queues keep filling up with a bunch of junk spam mail. It is addressed like it is coming from the postmaster on our server but it isnt. I have verified that i am not a open relay. I tried 3 different open relay tests and they all pass. We get our emails only through postini and i only allow their server ip addresses to forward into our server through the firewall. But i cant figure out where it is coming from. I just deleted over 180000 spam messages from the queue. The worst part is it keeps getting us blacklisted. Most companies are pretty nice and remove us quickly from the list but i'm sure they arent going to keep being that nice if i cant figure it out.