> On Feb 4, 2018, at 5:46 PM, J Doe <[email protected]> wrote:
>
> Feb 4 15:05:46 server postfix/smptd[718]: warning: hostname
> 1-2-3-4.dyn.isp.net does not resolve to address 1.2.3.4: 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
(NXDomain).
--
Viktor.
