RDNS_NONE hits when it shouldn't

Mark Sapiro mark at msapiro.net
Wed Oct 21 16:12:51 UTC 2015

On 10/21/2015 01:05 AM, gojensen wrote:
> We sometimes have issues with mail being flagged because of the
> RDNS_NONE (Delivered to internal network by a host with no rDNS).
> In essence this means that the senders IP address has no correct DNS
> setup. However, when we try do nslookup on the mailscanner machine with
> those IP addresses they resolve just fine.

That is not the issue.

A properly configured mail server will identify itself in HELO or EHLO
as say example.com.

dig A example.com

(or nslookup) will return 111.222.333.444 as the IP address of
example.com and this should be the IP address of the connecting server.
Then rDNS

dig -x 111.222.333.444

should return a PTR record back to example.com. RDNS_NONE says that
there is no PTR record in DNS for 444.333.222.111.in-addr.arpa.

See <https://en.wikipedia.org/wiki/Forward-confirmed_reverse_DNS>

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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