Exchange 2010 will not send messages

Exchange 2010

I can receive fine from all over the world, send messages internally but no luck sending externally to other domains.
I’m getting the 451 4.4.0 Primary target IP address responded with 421 4.2… unable to connect. For messages hanging in the queue.

On NSLOOKUP resolve distant domains fine, Server has a firewall rule allowing port 25, running Exchange diagnostics I do get ‘Remote server failed the mail acceptance test when trying to open the remote socket’, ‘remote socket not available’.

Install went fine with no issues, restarted Transport services several times, cleared the queue several times and resent messages only to see them hang.

Use MX record is checked, use ‘external dns’ is checked, etc.

So where do I look at next?
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Sounds like an issue with the send connector.

Start by performing a test at and share results please.
xmouserAuthor Commented:
I can't get to this as the business model does not allow access to the internet. I have many 'internal' domains available just not the internet.
You might have just answered part of the question then. Exchange requires HTTP/HTTPS, Port 25/587 to pass through. If you are unable, by policy, to do this, this could partially be why you're sustaining problems. Do you have any other exchange servers/domains?
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xmouserAuthor Commented:
Under server configuration > Hub transport > send connector:

Specify the FQDN this ... > Exchange server listed

Address Space:
Use DNS is checked. I also have Use external DNS lookup checked

Source Server:
The exchange server is listed.
xmouserAuthor Commented:

Other domains and servers available. I don't have access to them.
xmouserAuthor Commented:
Yes, port 25 was a thought but I do have a server firewall rule for that. I've sent a message to networking about port 25 to see if it's blocked.
xmouserAuthor Commented:
I am seeing this as well:

'A matching connector cannot be found to route the external recipient'
Definitely an issue with the send connector.

Either it's been modified, where you'll have to delete and re-create  using * in the address space.

Follow these steps:
I just realized I provided the wrong link above and fixed it. You will need to create/re-create the send connector and use the above link as a reference to properly configure it.

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xmouserAuthor Commented:
Got it thanks. I think I got it figured out but it'll be Tuesday until I can confirm.
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