i insatlled 2 new hub/cas servers with cas array, i added all exchagne DBs to new CAS array the old HUB/CAS server is also a 2010 so i wanted to remove the old server and use my new 2 arrayed servers so i removed the NAT from the old server to my public mail ip and i replaced it with a nat to my cas array ip mails are coming in but sending mails to outside is not wroking i get this error primary target ip address responded with:"451 5.7.3 cannot achieve exchange server authintication" i also have edge 2010 - new and is was working fine before this move so is it and edge configration problem the queue is in the hub/cas server

Check your receive connector on edge and see if you put any ip restrictions allowing only your old exchange server ip and update it. Step 4: Create a Receive connector configured to only accept messages from the Exchange organization You need to be assigned permissions before you can perform this procedure. To see what permissions you need, see the "Receive connectors - Edge Transport" entry in the Transport Permissions topic. This Receive connector requires the following configuration: Name From Internal OrgUsage type InternalLocal network bindings Internal network-facing network adapterRemote network settings IP address of one or more Hub Transport servers in the Exchange organizationAuthentication method Basic authentication over TLS James Chong MCITP | EA | EMA; MCSE | M+, S+ Security+, Project+, ITIL msexchangetips.blogspot.com

This problem occurs because the Exchange server cannot authenticate with the remote Exchange server. Authentication is required for Exchange servers to route internal e-mail messages between them. Please refer to the KB979175. Hope helps.Noya Lau TechNet Community Support