Exchange 2010 not sending external mail
Just setup Exchange 2010 on its own Windows 2008 Server, Installed no problem, setup Mailbox, Client Access & Hub Transport. Fine so far. Config Hub Transport to send & receive external mail as shown in Configure Internet Mail Flow Directly Through a Hub Transport Server: Exchange 2010 Help
I can send and receive internal mail fine, but mail to any external email account just sits in the queue with the error message "451 4.4.0 Primary target ip address responded with: 421 4.2.1 Unable to connect. Attempted failover to alternate host., but that did not suceed. Either there are no alternate hosts, or delivery failed to all alternate hosts."
I have checked the DNS and i can ping from the server to external addresses and the server itself fine.
Any Ideas? This is my first Exchange box and any help when be gratefully recieved :-)