451 4.4.0 primary target ip responded with 421 4.7.0. Too many errors on this connection


We are using Exchange 2010.  In last couple of days I have noticed emails gathering in the Queue.  Around 400 emails are there in Ready state.  Emails are flowing in and out but at a very slow speed and I have noticed the Queue goes up and down e.g. few minutes ago it was 417, now its 401..

I cannot figure out what is the cause.

Help please.

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Is this an Edge Server? The mails which are getting delayed are they for internet domains, and does the problem exist for all the domains or a particular domain. You could try telnet to that domain on port number 25 and see if its connecting. If it is not connecting them it could be problem with mail server at the receiving end.

Also, please try enabling message tracking log and smtp log. Send test mails and analyze the logs for any error. You can track mails using message tracking and see what error is reported.
fais79Author Commented:
I cannot tell whether the emails are to external or internal domain.. But the Delivery Type is showing as: "SMTP Relay to Remote Active Directory Site"

It's not an Edge but rather one of the two HUB servers and both show same in the Queues.

Many thanks for your help... I've spent hours and not getting anywhere...
You could double click on the queue name in queue viewer and it will open as another tab showing messages in the queue.

Since the queue is showing as SMTP Relay to Remote AD Site, it should be a connector to forward mails to another site. Do you have another site with exchange servers in your ogranization. If so, please try to telnet to hub servers in that site on port 25 and see if connectivity is working fine. Also, please check the network connectivity between the sites.
fais79Author Commented:
I double clicked on different messages and they seem to show the From address as from the public folders servers..

Did telnet test on port 25 and it connected fine..
These could be Public Folder Replication messages. Was there any changes done to Public Folders recently. For example a new Public Folder Replica has been added or a change in the Public Folder hierarchy. These kind of changes will trigger public folder replication messages that could impact network bandwidth.

Please refer following article for more information on public folder replication.


You could use Suspend-PublicFolderReplication cmdlet to pause public folder replication. This command will only stop content replication.


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