Hi Here is the Setup. 4 Exchange 5.5 sites connected through IMC. |-- Site3 | Internet ------Site 1-------Site 2------ | |-- Site4 Site 3 & 4 are configured to forward all mails to Site 2. Site 2 Configured to Route mails to site 1,3 & 4 Respectively. Site1 is connected to the internet Cloud & all External Mails of the organization enter & exit through the site1. I manage the site 2 .Exchange 5.5 SP4 running on Win2K SP 4.I was implementing VPN on the Exchange server .Added a Global IP on the Server & checked the VPN.Every thing works fine but the server becomes an open Relay .In IMC on the routing tab I checked Hosts & Clients with these IP addresses & Left it blank .Now the Server no longer relays but the problem is sites 3 & 4 are unable to send internet mails .Users get error 550 unable to Relay. Even adding the IP address of Site 3 & 4 Servers in Hosts & Clients with these IP box has not helped. Pls Help. Thanks Harry