Exchange Sending Errors

SBS 2011 with Exch 2010, not fully migrated yet, so the SBS 2008 with Exch 2007 is also on the net.  However, all email is being sent and received by the New Server.

On a few domains, I am getting this error (when sending looking in the Outbound Queue):

451.4.4.0 Primary target Ip address responded with "421.4.4.2 Connection dropped due to SocketError "Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts. "

On many domains, no problems at all.  Any ideas?

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Simon Butler (Sembee)Connect With a Mentor ConsultantCommented:
What is between the internet and the server? Firewall of some sort? I have seen this caused by a firewall scanning SMTP traffic.

Gareth GudgerCommented:
Is your new mail server sending out on a different IP than your old mail server? Are you using a Smarthost? Could be that your are getting blacklisted because your MX record does not match what you are sending from. Do you have an SPF record?
dougp23Author Commented:
Same EXTERNAL IP as before.  The INTERNAL non-routable IP has changed.  Not sure if that would account for anything.
Yes, a firewall, but the necessary ports are open.  No smarthost.
I don't think they have an SPF record.  

The whole migration was pretty nice, in that all the settings in the old Exchange came right over (Hub transport settings, etc).  

And it's strange how it is just one or two domains.  We can email hundreds of others without an issue.
Simon Butler (Sembee)Connect With a Mentor ConsultantCommented:
As long as the NAT is correct, then the internal IP address shouldn't be a problem.
Firewall - even with the ports open, firewalls can still cause delivery problems. Cisco ASA/PIX are the most notorious, but others can do it.

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