Hi, When should I use the "Principal name for proxy server" ? and should I do additional comfiure on FE server to enable this option for end users? Thanks.

Read this - http://technet.microsoft.com/en-us/library/aa996069(EXCHG.65).aspxSukh

Can you brief on your request please?

Some users out of our domain, but they need to use the outlook on their personal computer. In this case, I think they should enable the proxy to connect our exchange through RPC over Http. So I want to make sure whether we should do additional things on the exchange server to let end users use the proxy settings. If I am on the wrong way, please correct me.

You may refer to the Microsoft articles below for further information: Certificate Principal Mismatch http://technet.microsoft.com/en-us/library/aa998424(EXCHG.80).aspx Understanding Digital Certificates and SSL http://technet.microsoft.com/en-us/library/dd351044.aspx Fiona

As long as youhave implemented RPC/HTTP then is should be fine. - http://support.microsoft.com/kb/833401 Sukh