Hi Tom! OK. One more again ;-). You know in Outlook profile there are two different settings. 1) settings for Exchange proxy 2) settings for Exchange mail server 1) For the first settings (for Exchanage proxy) I mapped the external IP address of ISA server (DNS name for this IP address). This DNS has the name exchange.mydomain.com. This part works without any problem!!! 2) Outlook client needs to know the Exchange mail server name. It works ONLS and ONLY if I define on Outlook profile the mail server name of back-end Exchange server. THAT IS THE PROBLEM FOR ME!!! I expected that the back-end Exchange server does not neet to be known by clients. Microsoft Support Germany told that FE/BE design ist for OWA not for RPC over HTTPS access. They told that I must give the mailbox server name (in this case BE Exchange) in Outlook client on Exchange mail server field. What a FE/BE!!! Is that really correct what Microsoft Germany told? Best Regards Mustafa