Hi together! I have just solved this problem. The problem was the name resolving. I didn't use any split DNS before. I didin't modify also HOSTS file on the ISA server. It was the problem! I modified the HOSTS file. The record in this file was the pointing of NAT-Address of Fron-End-Exchange with Common Name. OWA works now well! Thanks for your response. Mustafa PS: I will describe my other problem in the next mail ;-) >>> RPC over HTTPS.