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

Marco d'Itri md at
Sat Aug 23 20:10:54 CEST 2014

On Aug 23, Doug Barton <dougb at> wrote:

> Fortunately SPF is dead simple,
Indeed, since SPF is dead simple it also has bad failure modes which 
break many common practices.
This is why DMARC best practices require to use both SPF and DKIM (which 
has different failure modes, but at least they can usually be blamed on 
bad software used by intermediaries) in the hope that at least one will 

> and DKIM isn't that much harder. In fact for
> one domain it's also dead simple (ProTip: Use OpenDKIM). I couldn't find a
The problem is managing it for tens of thousand of domains, when you 
often do not manage their DNS zones as well.
The support cost of teaching customers how to implement it is 
significant enough that for now blocking IPv6 to gmail is much easier.
(Also, if you manage just a couple of domains on your own personal 
server you will probably not have reputation issues with gmail, so this 
is barely relevant.)

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