Hi Greg, My scenario is to use an SMTP relay in a DMZ. This server has a public ip address. The external DNS server (Linux) has the public IP addresses in its database. My problem is not to receive or to send mails. I can use IMAP4/OWA/OMA/POP3 without any problem in my Exchange system. The problem is RPC over HTTP. If I try to create a new Outlook profile or try to access fron external network to internal, I can not connect to Exchange. There are following different error messages: "Invalid bookmark" "Outlook must be in online mode to connect to Exchange" "Exchange cannot be connected" Internaly I can use RPC over HTTP only if I give the back-end Exchange name in the mail server field (in Outlook client). Until now nobody gave any solution tip. I could not also find any good troubleshooting document in Internet. Microsoft troubleshooting article about RPC over HTTP is very common. There is also no document from Microsoft for example about "Invalid Bookmark" in an Exchange environment. Some questions: 1) Is there any connection between RPC Proxy server (front-end Exchange) configuration and MS Internet Explorer on server? If yes, what? 2) Is there any connection between ISAPI extension and RPC Proxy server? If yes, what? 3) Is there any connection between Tunneling TCP/IP protocol and RPC Proxy server? If yes, what? I think RPC Proxy does not function well also. Additionally I guess a DNS problem. Best Regrads Mustafa