> On Feb 4, 2018, at 5:46 PM, J Doe <gene...@nativemethods.com> wrote:
> Feb 4 15:05:46 server postfix/smptd[718]: warning: hostname 
> 1-2-3-4.dyn.isp.net does not resolve to address Name or service not 
> known
> Does this mean that:
> 1. smtpd receives a connection from an smtp client and does a reverse DNS 
> lookup
> 2. smtpd performs a forward DNS lookup on the result and compares the 
> resulting IP address to the initial IP
> 3. If the IP addresses don’t match it reports this error
> ... or is some other logic used to generate the error message?

The message happens when the hostname obtained from 1 fails to resolve
to an IP address that can be compared in 2.  The error is a hard error


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