When we send an email to particular two domains it is not delivering instead it helds up in the queue and throws an error message below and rest of the domains it is ok...it is not in the blacklist also 451 4.4.0 Primary target IP address responded with: "421 4.4.2 COnnection dropped." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts. we are using windows SBS server 2008 and we also applied the below solution still there is no go http://support.microsoft.com/kb/951291/en-us?fr=1 can anyone help me to resolve the problem......

Hi tmssupport1, Per your description, the issue related with SBS, you'd better to post it on the SBS forum. In my opinion, if just some particular domains could not receive your domain email, it seems that the recipient side block you domain, or your domain is listed in the public blacklist. Regards!Gavin TechNet Community Support

Hi tmssupport1, Per your description, the issue related with SBS, you'd better to post it on the SBS forum. In my opinion, if just some particular domains could not receive your domain email, it seems that the recipient side block you domain, or your domain is listed in the public blacklist. Regards!Gavin TechNet Community Support