Sam Jones:
> Good Afternoon,
>
> My senior tech and I have been having a squabble over PTR, Hostnames and
> reverse mapping.
>
> If you have a client connect from 1.2.3.4 and perform a host name lookup
> on that, so you get back host.example.com, would it impact on mail if a
> forward query for host.example.com returned multiple A records, say
> 1.2.3.4 & 5.6.7.8 alternating between the top of the result sets in a
> round robin?
With Postfix, multiple IP address per A record are fine, as long
as the CLIENT IP address is listed among them.
However, having multiple PTR records for one IP address, that is a
different matter. Postfix will not try to guess which name it should
use. It just takes the first name that comes up, and requires that
that name resolves to the client IP address.
Wietse
> I ask because we've seen an slightly odd pattern to some deferrals with
> a host where this happens and wonder if they may be using:
>
> reject_unknown_client_hostname feature, which requires not only
> that the address->name and name->address mappings exist, but
> also that the two mappings reproduce the client IP address.
> The unknown_client_reject_code parameter specifies the response
> code for rejected requests (default: 450). The reply is always
> 450 in case the address->name lookup failed due to a temporary
> problem.
>
> Sam
>
>
