@dansullivan
I've had your post moved to it's own thread.
On first inspection, it looks as if the connection is being closed before your MTA sends it's EHLO greeting. Have you tried a tracert to the exchanger from the affected IP.
Alternatively, you could try logging on to your MTA and run the command telnet mx.tb.ukmail.iss.as9143.net 25 to see if you get any connection at all..
Here's what you should see. Note that I sent the quit command to close the connection cleanly.
ravenstar68@box:~$ telnet mx.tb.ukmail.iss.as9143.net 25
Trying 212.54.56.11...
Connected to mx.tb.ukmail.iss.as9143.net.
Escape character is '^]'.
220 mx11.tb.ukmail.iss.as9143.net mx11.tb.ukmail.iss.as9143.net ESMTP server ready
quit
221 2.0.0 mx11.tb.ukmail.iss.as9143.net mx11.tb.ukmail.iss.as9143.net closing connection
Connection closed by foreign host.
Tim
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