Have installed a front end server in our domain and a new backend server, have made all the required configuration and have tried all permutation and combinations but to no avail. For background we had three exchange server working as backend as well as RPC proxy servers and RPC is working fine on all the three, we have introduced one new backend server and one front end server but outlook account on new backend server (on which we did no configuration for RPC proxy ) are not able to work from outside the domain. OWA is working fine from frontend server for users on new backend server. Have checked for the settings on front end server the valid port enteries are there on front end, able to access https://server.mydomain.com/rpc/rpcproxy.dll from out side, a blank page appears after authentication but the connection doesn't get through for Outlook client, have Integrated authentication configured on Backend server, have tried removing RPC on backend and 443 on backend (as read in technet article that RPC is not required on backend and front end makes coonetction on port 80 with backend server) but without any success. we are having Windows 2003 Domain all servers have Windows 2003 SP 2 applied. Exchange server is Exchange 2003 SP 2. Outlook Clients are Outlook 2003 SP 3 and Outlook 2007 SP 1.