Incoming SMTP in the year 2017 and absence of DKIM

Bjørn Mork bjorn at
Thu Nov 30 17:55:18 UTC 2017

Steve Atkins <steve at> writes:

>> On Nov 30, 2017, at 1:22 AM, Bjørn Mork <bjorn at> wrote:
>> "John Levine" <johnl at> writes:
>>> Broken rDNS is just broken, since there's approximately no reason ever
>>> to send from a host that doesn't know its own name.
>> rDNS is not a host attribute, and will therefore tell you exactly
>> nothing about the host.
> It tells you something about the competence of the operator and
> whether the host is intended by the owners to send email.

No.  It only tells you something about the administrative split between
IP address management and host management.

There is no way my laptop is going to be able to update the rDNS for all
addresses it will use in different networks.  This does in no way affect
its MTA configuration.

> Or, for a more empirical way to look at it, there's reasonable correlation
> between having missing, generic or incorrect reverse DNS and the host
> being a source of unwanted or malicious email.

Really?  Where did you get those numbers?  This is a myth.  Spam sources
are average Internet hosts.  The split between working and non-working
rDNS is mostly between IPv4 and IPv6, not between ham and spam.  And if
there is some correlation there, then I'd say that an IPv4 host is more
likely to be a spam source than a dual stack or IPv6 only host.


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