Re: [domainrep] rDNS identifiers

[Andreas Schulze <[e-mail]>]

Am 29.06.2012 12:37 schrieb Jacob R Rideout:
> Has anyone on the list considered the use of the IPv4 (or v6) PTR rDNS
> value as an identifier? Or more strictly, a fully qualified domain name, that also
> resolves to the queried IP address.

Hi,

MTX is (not very common) but much stricter.
see http://www.chaosreigns.com/mtx/

It's like a distributed selfmade whitelisting/reputation.

Consider I have an IP-Address 192.0.2.1 assigned to my mailserver. I like to send mail.
The receiver usually will reverse lookup that IP.
1.2.0.192.in-addr.arpa. PTR -> outbound-mailer.example.org.
That's all.

Next the receiver *may* doublecheck the name resolv too.
I personaly don't expect that the name resolv to 192.0.2.1.
If I would force that on my MX I would lose too much legit mail.
So the doublecheck is not practical for most people. So normal "dnscheck" ends with "sender has any rDNS".

But I as a sender could do more. I could state that I *do* have control over the dns zone
my PTR points to. That's usual if I own ip space. It's unusual for a dialup.

I can provide an A record 1.2.0.192.mtx.outbound-mailer.example.org. = 127.0.0.1
If the receiver ask for that record he knows that
 - I control the rdns zone
 - I control the forward zone
 - I really spend my time to setup such records.
The receiver may notice my much greater interest that my mails are delivered.

In fact that is a nice scheme to intoduce someone as a mailsender.
without having reputation history.
It definitly drops sender how do not control rDNS.

It does not pervent abusers to setup such records. But that ips could be blocked.
That's a decision every receiver could meet for himself. (or use a central blacklist)

Andreas