Exchange 2007 Sp3 on Windows Server 2008 R2

Error Some Domain

451 4.4.0 Primary target IP address responded with: ""421 4.4.2 Connection dropped due to ConnectionReset."" Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts

Is it only for one domain?

Check whether that domain IP is blacklisted or not.

Hi,

There could be many reasons on this issue. Most of them are Network or DNS.

So, please check your network first. And please disable any 3rd part AV temporarily to check this issue.

Also, please tell us more about your Exchange environment for us to troubleshoot this issue.

Best Regards.