Intra-Organization SMTP Send Connector between Exchange 2007 and Exchange 2010
Hello We're migrating an existing Exchange 2007 Server to a new Exchange 2010. I followed the documentations to setup the 2010 Server. Now, both servers have CAS, Hub and Mailbox Roles installed. Moved some of the mailboxes to the 2010 server. Incoming and outgoing mails are fine from both servers. The only problem which happens is, when someone with a mailbox on the 2007 server tries to send a mail to an user with the mailbox already moved to the 2010 server, the mails are hanging in the queue of the 2007 server with the "Last Error" message: 451 4.4.0 Primary target IP address responded with: "421 4.2.1 Unable to connect." Attempted failover to alternate host, but that did not succeed. Checked the Default Receive Connector on the 2010 Server. Both, Authentication => Excahnge Server and Permission Groups => Exchange servers are enabled. Enabled logging for the Intra Organization Send Connector: Set-TransportServer <2007 server> -IntraOrgConnectorProtocolLoggingLever verbose In the log i see messages like this: 2011-05-13T09:04:33.440Z,Intra-Organization SMTP Send Connector,08CDDF60F7A00B48,0,,<external IP>:25,*,,attempting to connect 2011-05-13T09:04:54.393Z,Intra-Organization SMTP Send Connector,08CDDF60F7A00B48,1,,<external IP>:25,*,,"Failed to connect. Error Code: 10060, Error Message: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond <external IP>:25" It tries to connect to the external IP address (which is the one used for OWA and so on, and is NAT'ed to the 2010 server). But no idea why. DNS is fine, checked that many times. Can connect without problems from the 2007 server to the 2010 server with telnet (IP, Hostname, FQDN). There is no firewall between the two servers (except the windows host firewall). Where does it gets the external IP from it tries to connect to??? After trying a lot of stuff i found in the net, i thought i got it. I entered my whole internal network at Organization Configuration ==> Hub Transport ==> Global Settings ==> Transport Settings ==> Message Delivery. After that, all mails where sent out to the 2010 server. Next morning i had a look into the queue of the 2007 server again, and there were new mails in the queue which could not be sent, with the same error as before. Found out that, when i restart the Exchange Transport service two, three or four times, the mails are sent out. After the mails were sent out it works fine for almost exactly 20 minutes and then stops again with the known error. Any ideas what that could be? Thank you very much Urs
May 13th, 2011 12:48pm

OK, got it. It was a DNS problem finaly. nslookup, telnet etc. always used the first DNS. But exchange seems to use an other one in the list sometimes even if the first one is reachable. Recognized that a collegue has added external DNSs to the list of internal DNSs after hours... (I think he has to invite me for lunch, at least one time...)
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May 13th, 2011 3:55pm

Hi, Thank you for sharing the resolution.Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. Thanks Gen Lin-MSFT
June 1st, 2011 7:26am

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