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reverse DNS issue

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  • reverse DNS issue

    Hi all,

    Recently, I have this reverse dns issue that the recipient end is rejecting mails from my side. After conversing with the recipient, it was found the ip address of my antispam box is different when their server did a reverse lookup of my box. The ip address they received happened to be my firewall. I did an online reverse lookup of the ip address my recipient received and it reported the correct server hostname.

    Before you can advise me what I can do, I probably need to tell all my current setup. I have a firewall facing the external world. Sitting behind the wall is my antispam appliance . My incoming/outgoing mails are routed through the antispam box.

    I am total noob about this and seek anyone's advice what I can do.


  • #2
    Re: reverse DNS issue

    You will need to ensure that the IP that is being rejected by the recipient (firewall IP?) has a reverse DNS entry.

    Then you need to make sure this reverse DNS entry has an associated 'A' record that in turn points back to the IP in question.

    Finally, make sure your EHLO greeting matches your reverse DNS value.

    See my article for more info:



    • #3
      Re: reverse DNS issue

      This usually means the NAT isn't correct somewhere.
      The traffic is coming out (and appearing to the remote end) as a different IP address. The remote end does a lookup on the IP address and gets a different result. They are not to know that you have multiple IP addresses.

      Simon Butler
      Exchange MVP

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