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Exchange Queue Backing Up

I am running exchange server 2010 and I am noticing quite a few emails that will not leave the queue because of this error: 451 4.4.0 Primary target IP address with: "421 4.4.2 Connection dropped due to SocketError"

I have tried creating a new send connector to force helo but that didn't work.
I am able to telent from the exchange server to a problematic domain. I can also do a nslookup without issue from the exchange server to a problematic domain.

Everything I am reading says this a DNS issue but I can't find where or what needs to be added\changed.
We have not made any changes to exchange and it's not all domains but it does seem to be getting more and more.

Thank you!
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1 Solution
AmitIT ArchitectCommented:
Who manages that problematic domain. 99.999% it is remote server issue or network or firewall issue.
WinsoupAuthor Commented:
I thought that too but the more I researched I saw people were able to solve issues by trying some of the things I mentioned.
Do you know what kind of problems they can look for? I can see if I can get ahold of their tech.
I know they are going to say that they are receiving emails from other domains so they probably won't do too much with it but I can try.
AmitIT ArchitectCommented:
From your side you can restart transport service and check again. If still, it shows same error, then you need to focus on network/firewall or remote domain server.
Alan HardistyCommented:
Check your Public IP Address on www.blacklistalert.org and see if you are blacklisted anywhere.

Also check on www.senderbase.org to see your IP Reputation to check that it is good,


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