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?