Exchange Error 421 4.2.1 Unable to Connect

I have 2 Exchange 2010 servers (EX01 and EX02) in a domain (Domain A). Hub Transport is installed on both and the DBs are in a DAG. Recently, we upgraded an Exchange server in a different domain (Domain B - same physical LAN) from Exchange 2007 to Exchange 2010. We essentially copied settings from the 2007 server to the new 2010 server in regards to Hub Transport, Receive Connectors, etc. During this time, the new server's IP address was and the old server (2007) was After all settings were configured, we swapped IPs and verified that MX records updated in each domain's DNS. The new server (2010) is now .40 and the old one (2007) was shut off.

Shortly after, we noticed that emails from Domain A are delayed to Domain B. Eventually, they do get through however. The error is the Queue viewer is "Primary Target IP address responded with: 421 4.2.1 Unable to Connect. Attempted failover to alternate host, but that did not succeed."

After some Google searching, I found the logs and found this...
2016-03-07T16:36:23.154Z,08D33CD71D67B094,SMTP,,>,Failed connection to (TimedOut:0000274C)[|MarkedUnhealthy|FailureCount:1|NextRetryTime:2016-03-07T16:37:23.154Z][TargetIPAddress:|MarkedUnhealthy|FailureCount:1|NextRetryTime:2016-03-07T16:37:23.154Z]
2016-03-07T16:36:23.154Z,08D33CD71D67B094,SMTP,,-,Messages: 0 Bytes: 0 (Retry : Unable to connect)

I noticed that sometimes it is trying to connect to which was the IP of the new 2010 exchange server before we swapped IPs. If DNS shows the correct IP to name translation, how is this happening? Where can I clear that entry?

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After completing Domain B's Exchange upgrade and the adjustment of the IP to  the the .40 as outlined above, did you restart the transport service on the Domain A Exchange servers?...

If not then I would recommend it to start with...
education-dynamicsAuthor Commented:
Yes. All exchange servers have been restarted since then.
Simon Butler (Sembee)ConsultantCommented:
Shutting off the old server is about the worst thing you can do.
If you don't want it any more then remove it using Add/Remove programs. Exchange expects all of the servers to be up and available.

I would also check DNS is correct throughout the domain, verify on the machines themselves.


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education-dynamicsAuthor Commented:
Anything specific I should be looking for in DNS? If I look at the DNS server in domainA, all records look correct. The mx records points to the correct exchange server name in domainB. A records in DNS for domainA for mail, www, owa, etc. all point to the correct IP (.40).
Simon Butler (Sembee)ConsultantCommented:
There should be no references to the old machine in DNS if it has been correctly removed.
The server real names should resolve correctly internally and for most implementations a split DNS used to ensure the external name resolves internally as well.

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