SMTP over IPv6 : gmail classifying nearly all IPv6 mail as spam since 20140818

Matthew Huff mhuff at
Sat Aug 23 20:31:33 CEST 2014

>From the blog:

"I have no reason to believe that this will really happen. People are already sending mail over IPv6 and I expect that the same reputation mechanisms used for IPv4 will be deployed as soon as they will be needed, with small policy changes to cope with the fact that end users typically get a whole network instead of a single IP address.

So I expect that DNSBLs will continue to operate as usual like they currently do for IPv4 addresses, optionally by promoting "single IP" listings to "whole /64" listings when appropriate."

Sorry, but it hasn't happened yet. It isn't computationally infeasible, it's that the implementations on the RBLS haven't caught up. Currently the backend for the RBLS in many cases are based on DNS resolvers such as bind, etc, which doesn't have a mechanism to return values for subnets, so until the RBL users add new features, test and roll them out, currently there is very limited IPv6 address reputation systems. Until there are, many mail systems are relying instead on rDNS/SPF/DKIM/DMARC. It's not an unsolvable problem it's just that it hasn't been implemented.

-----Original Message-----
From: at [ at] On Behalf Of Marco d'Itri
Sent: Saturday, August 23, 2014 4:05 AM
To: ipv6-ops at
Subject: Re: SMTP over IPv6 : gmail classifying nearly all IPv6 mail as spam since 20140818

On Aug 23, Michael Chang <thenewme91 at> wrote:

> I was under the impression that it wasn't so much about there being more
> IPv6 spam as much as tracking IPv6 reputation based on addresses was
> computationally infeasible.
This is a common myth: .


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