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e-mails being rejected from internal ip address

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  • e-mails being rejected from internal ip address


    i have an exchange 2007 server running on an internal ip address. The mx record at the isp has the external address and my router port forwards all mail to and from my mail server.
    Been up and running almost 2 years.
    Yesterday mail started bouncing from a certain domain (GMX) and the error message is that it is rejecting our ip address. It is the first time emailing this domain. E-mails to this domain are successful from web based email accounts.
    My mail server does not know anything about the external ip address that mail comes in and out of the building on and so does not include it in its EHLO - i'm wondering if this is the problem?
    Mail works elsewhere.
    Does anyone know why this is happening and ways round it? My isp don't really offer support when it comes to exchange server....

  • #2
    Re: e-mails being rejected from internal ip address

    The fact that you are using Exchange is immaterial.

    You need three things to email most servers.

    1. A valid DNS host that points to your server (even if this is a NAT to your external IP address).
    2. A valid PTR record that points to your server and has a matching DNS host. Your ISP will set the PTR record for you.
    3. A valid ehlo entry set on the Send Connector. The ehlo should match the two above.

    Any of those three are invalid or doesn't resolve to the correct external IP address then remote sites will reject the email.

    Simon Butler
    Exchange MVP

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