What kind of mail server were you running prior to installing Zimbra? Perhaps your previous mail server was hijacked and used as a SPAM machine without your knowledge?
Have you contacted CBL and had your IP removed from their list?
As far as your firewall goes, I think Phoenix is asking you whether or not Zimbra and IPTABLES are running on the same computer. Are they?
"Let's look at this from a standpoint of "Status". What exactly, on the Space Craft, IS working?"
-Flight Control, Apollo 13