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I'm looking for a way to make Exchange 2007 only accept mail from a certain group of hosts. These hosts all use the same identifying rDNS entry.

Exchange 2003 uses a whitelist based on the reverse DNS, there we could add the hostname to the to the "Domain" field.

However, in Exchange 2007 this option seems to be removed. Is there a way to do this?

IP's however tend to change. These changes can occur at any time, and it is impossible to keep all the servers up-to-date to the new IP's.

Running a script that resolves the hostname and whitelists them accordingly is my last-resort option, but this is not fool-proof.

Does anyone know whether this is possible and if so, how?


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2 Answers 2

Exchange 2007 doesn't have a built-in way of doing this. The rule that'd have to have it would be the Receive Connector, and those only take IP data. That leaves external means of doing it, such as your batch-mode updater script, or a net-security device of some kind that can take hostnames and not just IP addresses in its ACLs.

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It is generally a bad idea to rely solely on reverse DNS to control email relay permissions; it's not locked down the way that forward lookups are. Anyone who controls it can configure the reverse records to be in your domain if they want to. It sounds far fetched but spammers have been known to do this in the past.

You might want to look into using SMTP authentication instead. That will allow your servers to send from any IP address with minimal hassle.

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SMTP auth is not available (yet). The servers that will deliver mail are appliances and basically blackboxes. –  user45577 Jun 14 '10 at 7:08

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