[Mailman-Users] DMARC and Gmail

[Mark Sapiro]

On 04/16/2014 06:58 AM, Lindsay Haisley wrote:
> Has anyone seen issues with Gmail accounts and Yahoo's DMARC policy?
> I've been working with the list admins of one of FMP's hosted lists and
> they've seen over 100 addresses unsubscribed from the usual suspects -
> yahoo.com, att.net, Comcast, etc., but no Gmail accounts and there are
> 228 of them on the list.


This is consistent with what I've observed on lists.


> Nonetheless, the PC World article at
> http://www.pcworld.com/article/2141120/yahoo-email-antispoofing-policy-breaks-mailing-lists.html
> lists Gmail as being one of the cooperating email service providers
> honoring Yahoo's DMARC p=reject policy.


I've done some testing. If I send a message from my server, but not from
a list From: a yahoo.com address to a gmail address, it gets rejected with

> 550-5.7.1 Unauthenticated email from yahoo.com is not accepted due to domain's
> 550-5.7.1 DMARC policy. Please contact administrator of yahoo.com domain if
> 550-5.7.1 this was a legitimate mail. Please visit
> 550-5.7.1  http://support.google.com/mail/answer/2451690 to learn about DMARC
> 550 5.7.1 initiative. uc7si1048327pbc.131 - gsmtp

However, if I send the same message to a list which then resends it
without touching the From: to the same gmail address, gmail accepts it
and delivers it to my gmail spam folder.

Thus, it appears that gmail does honor DMARC policy in general, but has
some kind of mitigation policy to identify (heuristicly? via headers?)
mail from a list and quarantine it even if the From: domain's policy is
reject.

Note it doesn't use the RFC 2369 List- headers because it still
recognizes a message without them as from a list.

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