I'm not sure what happened. Previously the only WAN public IP returned by PHP's $_SERVER['REMOTE_HOST'] was the firewall's. All LAN client private IPs were already visible. Now I'm suddenly seeing WAN client public IP's via that server variable. I didn't change anything on the MX.   Thank you for helping. You clarified that the MX is already configured as needed. I'm wondering if there's something in IIS that maybe mucking things up. ... View more