On 23/10/20 2:26 pm, Bob Proulx wrote:
The tragicomical thing is that Gmail does follow policy and when the
policy of the sending site is strict DMARC and the mailing list does
not rewrite then Gmail subscribers to mailing lists will get
automatically unsubscribed when/if the bounce ratio exceeds the
threshold! That's perhaps a surprising unintended consequence.
Because the sender's message from the mailing list re-sent to the
Gmail subscriber is bounced by Gmail back to the mailing list then the
mailing list management software counts it as a bounce from the Gmail
end against that subscriber. The sender is unmarked. So it depends
upon the amount of mailing list traffic and the ratio of mail from
strict DMARC sites and not strict. A large flow of non-DMARC traffic
will keep the ratio low. But then if on a single day even one strict
DMARC sender sends many messages causing many bounces it will trip
over the threshold for the Gmail subscribers and result in all of them
being unsubscribed all at once.
And then a bunch of Gmail subscribers are all left wondering why they
were unsubscribed. Sometimes they will even write in to the list
admins asking that question. Yes these are actual events.
I think the best compromise is that mailing lists must rewrite the
headers when handling mail from sites with a strict DMARC policy.
Although there are others that have disagreed and wished their email
to be discarded rather than modified in any way.
Provided that domains which publish strict DMARC policies sign their
emails correctly with valid DKIM signatures that pass the DMARC
alignment test, and the mailing list software rewrites the envelope
(5321.MailFrom) sender, then the email will still pass DMARC check.
The problem is sender domains that use strict DMARC policies and either
don't use DKIM or fail the alignment test.
FYI For a while I was emailing individuals on this mailing list when I
noticed this sort of thing, and more often than not the recipient was
receptive to my input, and in a position to be able to fix the issue,
and was willing to do so, which is a win for everyone! Unfortunately,
lately I haven't had the time...
/[Rhetorical q//uestion to everyone] Have you checked your DMARC lately?
;-)/
Nick.
