I have a spam appliance in front my my zimbra. The firewall does a clalout for every mail to see if the user actually exists before processing hte mail..which works for me. however what i have found is the zimbra machine is accepting all connections irregardless of if the recipient mailbox exists or not. The mail server then rejects the mail and bounces it back to the firewall. What i need the mailserver to do is to reject invalid usernames at this clalout point so that the invalid mail isn't being sent to the zimbra box at all. How can i accomplish this?