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451.4.4.0 Primary Target Ip address responded with 421 4.2.1 unable to connect

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  • 451.4.4.0 Primary Target Ip address responded with 421 4.2.1 unable to connect

    We have recently deployed our Exchange 2010 SP1 running on a single server. Since going live i have noticed that some mails are getting stuck in the mail queue and have the following error in the log.

    451.4.4.0 Primary Target Ip address responded with 421 4.2.1 unable to connect

    This only seems to affect some domains and not others, most outgoing mails to remote domains work fine. I have checked our reverse look up records and its pointing to the correct to record, i.e our server. I have checked on numerous blacklist checkers and our IP is not blacklisted anywhere on the net.

    I have noticed that for some reason it almost always appears to affects client emails that have there mail spam filtering provided to Message Labs. I have spoken to them and i have given them our ip and they say it all checks out and not black listed anywhere.

    Our server itself is hosted behind a watchguard x550e firebox, our mail spam filtering is provided by a 3rd party company with our mx records pointing at them. They then forwards messages to us, this works fine, but when we send emails to clients that use message labs they get stuck in the queue. Is there anything that we need to do to our outgoing send connector or firewall. At present our send connector is not configured to use Enable Domain Security (Mutual Auth TLS

    Has anyone else had this problem and how to fix it, as there doesnt appear to be much on the net about this error.

    Thanks

  • #2
    Re: 451.4.4.0 Primary Target IP address responded with 421 4.2.1 unable to connect

    Can you not send your email out through the third party anti-spam service? Surprised Message Labs actually talked to you, because normally they will not unless you are a customer. They are probably doing some kind of call back to see if your server is listening for SMTP traffic, which of course it will not be because of the use of the third party service.

    Simon.
    --
    Simon Butler
    Exchange MVP

    Blog: http://blog.sembee.co.uk/
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