SMTP Relay to Remote Active Directory Site.” and the last error is 451 4.4.0 Primary Target IP address responded

hi guys

I have two sites both on Exchange 2010, both on Windows 2012 R2. I've attached a screenshot of what I am seeing in the queues from Site B to Site A. Port 25 is definitely open. I can telnet. I have restarted both servers. So I don't understand what on earth is going on and why these queues are occurring.

I read that it could be self signed SSL related? So I've tried re-applying the SMTP service to the current certificate and restarted the Transport services, but still these queues remain.

Any help would be greatly appreciated guys,

Thanks for helping
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arnoldConnect With a Mentor Commented:
It is not a standard error message do it is likely an issue of anti-spam.

From your exchange system telnet to the other port 25  of the other
The issue might be in the inter-exchange connectors.
Mimic an SMTP session,
ehlo exchange_server_name
mail from: <youremailaddress>
rcpt to: <recipient_address>
From: sender
To: recipient
Subject: test message

This is a test


See what response you get.

You have to check logs on both sides.

It is unclear to me which server is the 421 error from.
The sending server that fails to connect and has a permanent error. Or there is something in the path that causes this error.
Jason CrawfordConnect With a Mentor Transport NinjaCommented:
It looks like email is routing via site links.  Try this:


followed by

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YashyAuthor Commented:
Hi Arnold,

II'm trying to do Telnet sessions on both Site A and Site B. I am at Site A and Site B is where I took the snapshot of the queues from. I keep getting 'Unrecognized command' at both sides when I get to the part where I am supposed to enter 'ehlo server_name'. Once I try again, it goes to the next bit. I'm not mistyping anything either. I get to the part of the body and after I enter the '.' and hit enter, nothing happens. This is on both sides. Bizarre.
YashyAuthor Commented:
At Site B (which is where I believe the problem may lie), the logs shows 'Inbound authentication failed with error UnexpectedExchangeAuthBlob for Receive connector Default name_of_server.
YashyAuthor Commented:
I'd like to give points to the other guys for their help.
YashyAuthor Commented:
I managed to solve the issue, but would like the other guys to get points for their contribution.
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