451 4.4.0 Primary target IP address responded with: "421 4.2.1 Unable to connect. I have a scenario that I have old exchange 2003 server which is still using to send the email and the new exchange server 2007which has all the mail boxes. I could not change it until I sorted out with Symantec mail security.
Mails are going to 99% domains but not going to very few domains and for these domains the above message coming. If someone could help in this regard.
Could it be due to some SPAM black listing on these sites. I have also check www.mxtoolbox
for blacklisting and it does not mention any site which blocks our domain.