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

[Mark Sapiro]

On 04/15/2014 06:50 PM, Conrad G T Yoder wrote:
> 
> So it really doesn’t affect domain email hosted by Yahoo such as att.net, sbcglobal.net, ymail.com, etc?  Yahoo has not added a dmarc p=reject record for email from these domains? 


Short answer: That's correct.

Long answer:
mark at Notebook-09:~$ dig +short txt _dmarc.ymail.com
"v=DMARC1\; p=none\; pct=100\; rua=mailto:dmarc-yahoo-rua at yahoo-inc.com\;"
mark at Notebook-09:~$ dig +short txt _dmarc.sbcglobal.net
mark at Notebook-09:~$ dig +short txt _dmarc.att.net
mark at Notebook-09:~$

The above means that ymail.com publishes a DMARC p=none policy and
sbcglobal.net and att.net publish no DMARC policy at all, so while those
domains may honor the DMARC policy of the From: domain for incoming
mail, mail From: those domains is currently unaffected.

Note that ymail.com does request aggregate reports to be sent to
dmarc-yahoo-rua at yahoo-inc.com which means that failures will be reported
even if they don't affect mail delivery.

Note also, that sec 6 of the draft DMARC specification
<https://datatracker.ietf.org/doc/draft-kucherawy-dmarc-base/> says in part:

   Mail Receivers MAY choose to reject or quarantine email even if email
   passes the DMARC mechanism check.
   ...
   Mail Receivers MAY choose to accept email that fails the DMARC
   mechanism check even if the Domain Owner has published a "reject"
   policy.

so no one is REQUIRED to honor DMARC policy, and even domains which
publish a DMARC policy are free to ignore the DMARC policy that should
apply and accept, reject or quarantine any particular incoming message
for other reasons.

-- 
Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan