Re: DMARC and yahoo

Michael Richardson <mcr+ietf@sandelman.ca> Wed, 16 April 2014 02:23 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: "Theodore Ts'o" <tytso@mit.edu>
Subject: Re: DMARC and yahoo
In-Reply-To: <20140416012205.GC12078@thunk.org>
References: <CAKW6Ri6OUmxGaBOGR2hoWpDOGWsVQ9tQ2Q9ogkT5wzFhFJLBbQ@mail.gmail.com> <534D9C2C.8010606@gmail.com> <20140415214348.GL4456@thunk.org> <1397607352.389753533@f361.i.mail.ru> <534DCFFB.4080102@gmail.com> <20140416012205.GC12078@thunk.org>
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Date: Tue, 15 Apr 2014 22:23:22 -0400
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Theodore Ts'o <tytso@mit.edu> wrote:
    > This means that if a bob@yahoo.com sends a message to a list which
    > includes alice@hotmail.com, and the mailing list server keeps the from
    > field as "bob@yahoo.com".com", and sends the message to all of the mailing
    > list recipients, which includes alice@hotmail.com, the following things will happen:

    > a) hotmail.com will compare the sender address (authenticated with
    > SPF) with the from address (authenticated by DKIM), see that they
    > are different, and since yahoo.com has a DEMARK p=reject,
    > hotmail.com will bounce the mail.

    > b) this means alice@hotmail.com will never see bob@yahoo.com's mail

    > c) since the mailing list server receives a bounce from hotmail.com,
    > if there are enough attempts from yahoo.com users to send mail to
    > the mailing list, the number of bounces will cause the mailing list
    > server to suspend or remove alice@hotmail.com from the mailing
    > list.

So, as a WG chair, a person known to me just tried to post to the list
From a brand new yahoo.com mail account.  They aren't subscribed with that
address.  I would normally just approve, and add them...

It seems to me that I must now actually reject, because it would affect other
subscribers.

I'm now thinking that we need to remove all the @yahoo.com addresses from
posting to ietf mailing lists.

--
Michael Richardson <mcr+IETF@sandelman.ca>ca>, Sandelman Software Works
 -= IPv6 IoT consulting =-