[Mailman-Users] Emails from yahoo members, are getting rejected by yahoo, "Service Unavailable".

Stephen J. Turnbull turnbull at sk.tsukuba.ac.jp
Tue Apr 15 05:33:00 CEST 2014

Keith Bierman writes:

 > While the process of revising the RFC should have been followed,

No revision of the RFC was made, and Yahoo! followed the RFC in
updating its own DMARC policy.  That's where DMARC sucks[tm].

 > it does seem that they are trying to solve a real problem.


 > Mail should come from who it says it comes from, not make it
 > trivial to pretend to be someone one isn't.

Well, maybe.  But DMARC doesn't solve that problem.  It's still
trivial to pretend to be someone you aren't.  Just get an address at

I suppose what you mean is phishing, ie, pretending to be a specific
other someone.  Well, if you want to be sure of identity, insist that
your correspondents digitally sign their mail.  Effective checks must
be done in the MUAs because it's still very easy to spoof somebody
(use "Chase Bank" <chase-bank at 0xdeadbeef.my>, for example) even with

What needs to be done to make this user-friendly is for the MUAs to
provide a simple way to configure "trusted partners" such as your bank
and your psychotherapist.  The bank would probably be very easy (it
uses DKIM so the MUA can check it).  Web-based MUAs can do this for
you (Google's "Gold Key" program).  The personal relationship problem
is harder, but basically you need a convenient way to distribute PGP
public keys and add them to specific correspondent records.

For licensed professionals, governments could maintain third-party
authorization mechanisms a la OpenAuth.

 > So why not adopt a standard where the *sender* is always the list?

Because Internet mail makes a specific distinction between *sender*
and *author*.  we already *have* a way to identify the *sender*, and
we already *do* identify the list as the sender IIRC (Resent-*
headers), and in most cases we do make it clear that the list is a
list (RFC 2369 headers).  However, in their bottomless contempt for
the average user, the DMARC authors chose to insist on authenticating
the *author* with the *sender's* credentials because that's the best
that can be done without cooperation from the recipient and her MUA.

 > The obvious downside is that "reply to poster" stops working, but
 > do these "security" tools care if the reply-to is different from
 > sender? if the list default is "reply to poster" set the reply to
 > as the original sender, but "correctly" identify the message as
 > coming from the mail server automation ... not the original sender.
 > Other than noncompliance to the existing RFC(s), what am I missing?

Nonconformance to RFCs means that you break all conforming
implementations.  "Reply-To Munging Considered Harmful" is just the
start.  Internet governance is based on the RFC process.  If you allow
large companies to disregard RFCs for their convenience, they *will*
break things badly.  (Small companies will break things, too, but not
so badly.)

Note that Yahoo! has initiated a denial of service attack on millions
of innocent list subscribers.  *This is not a one-time problem.*  This
will happen again every time a new domain changes its policy to
reject, because even if we break *future* Mailman to conform to
Yahoo!'s Brave New World, *past* Mailman installations will continue
to exist and many of them will have taken stopgap measures (eg,
moderating all Yahoo! subscribers).  We have to take a stand against
this kind of behavior.

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