I have a problem with sending mail to a specific external domain from exchange 2003. Mail sent to any address at that domain just sits in a queue until it eventually generates an NDR with status number 4.4.7.
The error message for the queue just says 'An SMTP protocol error occurred'
I found a couple of kb atticles relating to this error but they seem to be about open relays and I know the exchange box is not an open relay.
I can send mail to this domain from a hotmail account so I know the address is correct.
I'm new to exchange 2003 so I'm a bit stuck as to where to look.