Re: [DNSOP] I-D Action: draft-ietf-dnsop-isp-ip6rdns-03.txt

Philip Homburg <> Sun, 14 May 2017 10:16 UTC

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Cc: Lee Howard <>
From: Philip Homburg <>
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Date: Sun, 14 May 2017 12:13:30 +0200
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Subject: Re: [DNSOP] I-D Action: draft-ietf-dnsop-isp-ip6rdns-03.txt
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>>we will never know, because every v6 end system will have a ptr, either
>>naturally, or machine-generated for it, because v6 providers will not
>>want their rank-and-file v6 endsystems to be excluded from important
>>activities such as transmitting e-mail.
>If =B3v6 provider=B2 includes =B3residential ISP=B2 (the topic and audience=
> for
>this draft), then the inability to transmit email is by design.
>That is: ISPs commonly prevent residential users from sending email (by
>default). They say this in their Terms of Service, they block port 25, and
>they don=B9t publish PTRs. This is consistent with recommendations by
>M3AAWG[1] and BITAG[2], for instance.

>People who run mail servers generally understand these limitations. The
>BITAG paper does recommend clear disclosure and methods to opt-out. Makes
>sense to me: I want a human decided they want their system to send mail,
>not a bot.

I wonder if with the EU netneutrality laws it is possible to have a blanket 
block if port 25 outbound. 

Historically, many ISP that wanted to upsell business accounts would
actually block port 25 inbound. Which does prevent relays but not bots
sending spam.

Of course having an option where the customer can request to port to be
opened and then have it closed by default is best. But that may be too
expensive for many ISPs.

But my goal was not to say something about whether port 25 should be
blocked or not. But just that based on todays internet and spam filtering,
if an ISP allows customers to send mail, then the ISP has to provide
the customer with a way of setting up reverse DNS.

I don't really care whether a reverse DNS check is good or bad when it
comes to filtering spam. It is just a reality that enough parties are
using such checks that without reverse DNS you have a serious issue
getting mail delivered.