SBS 08 Server routes all outbound mail via smarthost to Postini. Mail delivery stopped today. The Exchange queue has the error 451 4.4.0 Primary Target IP address responded 421 4.2.1 unable to connect. Confirmed with Postini that there are no issues and other clients using same setup are working fine.
I cannot telnet to port 25 at all from the server to any mail host. Firewall rules allow all outbound and nothing was changed prior to this happening. Rebooted router, firewall and server. If I remove the smarthost, delivery via DNS to recipient servers also fails (due to no outbound on port 25). Web browsing works fine from server. DNS resolvers all work fine. Inbound mail is working fine. I am stumped.