The old 421.4.2.1 Error!

Home Forums Messaging Software Exchange 2007 / 2010 / 2013 The old 421.4.2.1 Error!

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    Alrighty, we have one domain that we try to send to where everything fails to go through.

    Checking the queue it shows:
    “451 4.4.0 Primary Target IP address responded 421 4.2.1 unable to connect. Attempted failover to alternate host, but that did not suceed. Either there are no aternate hosts or delivery failed to the all alternate host.”

    I thought it may be a resolution issue but the domain does pull up. I even added external DNS servers as a test (in case out internal DNS couldn’t resolve).
    Telnet works fine.
    No firewall issues.
    No antivirus issues either.

    I ran some DNS tests on this domain and it shows no reverse DNS – the only issue.

    Cannot determine anything else to get the messages to go through. They can send to us though…

    Called the client and they stated they receive email from other companies…

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