Mail between two exchange internal exchange boxes fail.

OK.  Here's the setup.  I have an environemnt with two servers that are twins in HW and SW.  The SW is as follows;

Windows 2003 R2 Enterprise Edition
Exchange 2003 Enterprise Server SP2

Server A and Server B

Server A is an older server.  We are moving some of the mailboxes from A to B.  After moving a test batch of users we begain to test, and here's what we have.

Mail from server A can go to server B without a problem.
Mail from B heading to A sits is a queue and is undeliverable with the following error a the queue *The connection was dropped by the remote host".  Server B can send and receive external email, but cannot send to server A.  The message gets queued and eventually times out.

I'm not sure where the issue is. DNS seems to be working OK, as are all other network functions.  No errors in the event log at all.

Any help would be greatly appreciated.

Thanks in Advance...
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Old UserCommented:
Have you checked your connectors?
mrodriquesAuthor Commented:
I'm not the person who usually takes care of the exchange servers here.  I was thrown into this one.  When I look in "routing groups/connectors, there are none listed.  Did one need to be added when the second server was added?
In defailt SMTP server, access check connections should be all except the list below. On server A.

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mrodriquesAuthor Commented:
That seemed to resolve the issue.  There were several IP addresses listed in there.  Some were routable, some were non-routable.  When I flipped it and restarted the cirtual servers mail began moving again.  Thanks for the help.  Why would those addresses have been listed?
To accept connections from certian ip address..
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