421 4.2.2 Connection Drop due to Timeout on Exchange 2010 Hub Transport

I have an Exchange 2010 Hub Transport in SiteB that is routing smtp email to our Exchange 2003 server in SiteA for the same domain. I am starting to see delays in emails from Site B to Site A. I look up the message queue and I see messages with the last result being 421 4.2.2 connection drop due to timeout.  The messages seem to eventually send to the Site A server. The connection from Site A to Site B is over a MPLS connection.

What test can I perform to determine if the issues is configuration, network, server, or DNS?
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gregurlAuthor Commented:
I went to the Exchange 2003 Default SMTP connector. I noticed I do see the Exchange 2010 Hub transport server listed in the current sessions, but I see the connected time is adding up and eventually seems to end at around 600 seconds which is the timeout on the SMTP on Exchange 2003. So, it seems the Exchange 2010 can sort of connect to the Exchange 2003 but the connection is not completing.
you second note is right, becasue the message confirms that the connection was created then it was dropped, due to timeout,
I think if it's not a physical connection issue, then you can try checking EHLO, HELO Settings in both servers
back to your original question:
first DNS is not the issue, becuase the connection is stablished,
raise the logging level for smtp in exchange 2010 and check any of the sessions to decide  the next step, i.e after session started after how much time exchange 2010 tried send the SMTP commands

is there any proxy, firewall involved?
also try to remove TLS from both settings and see what happends

good luck

gregurlAuthor Commented:
I decided to restart the Hub Transport server and the mail seem to flow without delay.

I will monitor for the next week to see if the queue builds up.

The only thing that may have happened is a couple of weeks ago the connection from Site A to site B was lost for about 6 hours, but everything seem to come back online after the network line was back up. I got a few help desk tickets about slow delay this week and that is when I saw the queue building up.

I still did not find a definite solution to the error in question.

For now,  I will wait and see what happens.

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gregurlAuthor Commented:
The final resolution or cause was unknown but a restart of the serve fix the issue for now.
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