I've been banging my head against this for some time now. basically I've got an exchange 2003 server inside my network that goes through the firewall to the DMZ where the inbound and outbound mail hits a spam filtering appliance, the mail should then go from that spam filtering appliance out to the internet. our mail headers on outbound mail confirm this but the referenced IP address is wrong causing RFC's to fail and blocking our legitimate email from specific destinations. does anyone know what could cause this. I've already reviewed the firewall and nat rules on my Firewall and could find nothing there. in fact a packet trace using source and destination addresses says it's natted as I expect it to be, but the mail headers still use our internet ip address instead of the one dedicated for email.