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

[Stephen J. Turnbull]

Sylvain Viart writes:
 > Le 18/04/2014 09:41, Alain Williams a écrit :
 > >> I may have missed some topic, but why SRS
 > >> (http://en.wikipedia.org/wiki/Sender_Rewriting_Scheme) doesn't
 > >> come to rescue here?
 > > SRS rewrites the *envelope* sender.
 > >
 > > My understanding is that the YAHOO DKIM uses the From: header,
 > > not the envelope sender.
 > 
 > Oh I see. Thanks.
 > So to use mail's Header terminology, only the Return-path: is modified, 
 > not the From:

No, the envelope sender often does end up in Return-Path, but it need
not.  The envelope sender is the entity in the SMTP "MAIL FROM"
command, not anything in the headers.

 > Is this related to DMARC in general?

Yes.  DMARC is designed to work with "From alignment", that is,
authenticating the domain in the from header.  It *can* also
authenticate the mailbox using DKIM, but there's no guarantee that a
third party can see.

The reason for this is that the DMARC authors are concerned about
phishing, which basically works by sending a fake "From".  Therefore
they want to ensure that only the real domain can send "From" that
domain.

 > May be not corrected by SRS, because of DMARC is more recent than
 > SRS…

They're completely unrelated.

 > Or this is a yahoo challenging with a somewhat too strong
 > configuration?

Yahoo is following the DMARC standard.  They don't believe it is "too
strong".  See above.