[Techtalk] Opinions/Experiences Needed: Mailing list bouncing problem

[Terry]

Hi folks,

LinuxChix had an issue earlier this week with the Newchix mailing list
where over 200 members had their subscriptions disabled due to bounces.
 We re-enabled everyone's subscription and tracked down the problem.
Unfortunately, it wasn't a glitch in our system.  We violated Yahoo's
DMARC policy because we use the poster's address in the From:header.  To
mitigate the problem, we've changed the bounce processing options for
our mailing lists until a solution can be implemented.

To keep this message as brief as possible, this is not a technical
discussion of DMARC, DKIM or SPF but rather a discussion on the
practical impact on LinuxChix's mailing lists and members when a domain
has a DMARC policy of reject.

Yahoo's policy: See https://help.yahoo.com/kb/SLN24016.html.
"In 2014 Yahoo updated the DMARC record with "p=reject" for the
"yahoo.com" domain.  This means all DMARC compliant mail receivers
(including Yahoo, Hotmail, and Gmail) are now bouncing emails sent as
"@yahoo.com" addresses that aren't sent through Yahoo servers. Any
messages without a proper Domain Keys Identified Mail (DKIM) signature
or Sender Policy Framework (SPF) alignment will be rejected."

Yahoo is not the only mail provider to implement a DMARC
reject/quarantine policy nor is it the only one with DMARC compliant
mailservers.  At least 49 domains on LinuxChix mailing lists are DMARC
compliant. As best we can tell, *this affects at least 65.5% (1,555) of
our members*.

The bottom line is that DMARC breaks mailing list software, including
Mailman.  See this post:
http://www.circleid.com/posts/20140408_yahoo_addresses_a_security_problem_by_breaking_every_mailing_list/

We're not the first list this has happened to. See
http://www.gossamer-threads.com/lists/nanog/users/175053 for an
enlightening discussion on the NANOG list. There's been a huge amount of
debate about this. If you want hours of reading fun, search for "DMARC
and Mailman".  The purpose of this email is not to reignite the debate
but to:

1. Ask for your opinions on how LinuxChix should handle this because it
will affect our members, and
2. Solicit any experiences you may have had on other mailing lists in
relation to the DMARC issue.

The problem for LinuxChix is three-fold:
- legitimate mail isn't getting through,
- the bounces are disabling members' subscriptions, and
- we risk getting blacklisted due to "excessive bouncing therefore we're
spamming" or "you're a spammer because you keep showing up in our held
messages/junk folder".

Mailman has been patched for DMARC compliance, offering two methods. One
is called "from_is_list" and implements DMARC compliance for *all* posts
with two options:

- Rewrite the From: header with the poster's name 'via the list' and the
list's address and merge the poster's address into Reply-To:
or
- Wrap the message as a message/rfc822 sub-part in a MIME format outer
message with From: and Reply-To: as above.

Mailman does not recommend "from_is_list" because, as best as I can
figure out, while all messages become DMARC compliant, you then break
RFCs and you should break RFCs only when there is no other choice.

The second, "dmarc_moderation_action", *selectively* acts on poster
domains with a DMARC policy of reject or quarantine.  It has five options:

- the two above
- accept
- reject
- discard

The LinuxChix sysadmins and coordinators are now considering how to
handle this.  Each method and each option has practical effects for our
members.

Accept - This, in effect, changes nothing as this is what we're doing
now.  Mail from members with Yahoo, et al, addresses will still be
bounced by any DMARC compliant receiving server (Gmail, Yahoo, Hotmail,
etc).  Our list admins will need to deal with all the bounces and
re-enabling of subscriptions, unless we turn off bounce processing.  In
short, it does nothing to solve the problem and increases the burden on
the sysadmins and mailing list admins.

Reject - Reject messages from a poster with a DMARC policy of
reject/quarantine with an explanation as to why.  This would affect
10.57% (251) of our members.

Discard - Drops any message from a poster with a DMARC policy of
reject/quarantine.  Same as rejecting, 10.57% (251) of our members, only
they'd have no clue.

Munging/Wrapping - Both of these options impact all members because both
change the Reply-To and From headers.  If done selectively, only
messages from domains with policies of reject/quarantine will be
changed.  The message From: header would be "abc via techtalk
<techtalk at linuxchix.org>".  Reply-To would be abc at yahoo.com AND
techtalk at linuxchix.org.

Currently, the poster's address is in the From: header and utilizing the
Reply-To function in your mail client will result in the message being
directed to the original poster.  If we munge or wrap, the Reply-To will
now go to the poster AND the list.

*This is a significant deviation from how our lists currently work.*  We
assume a private reply unless Reply-To-All or Reply-To-List is used.
This could result in someone replying to the list inadvertently when the
reply was meant to be private.
See http://archive.linuxchix.org/reply-policy.html.

*Depending on how you filter (if you do) LinuxChix messages, this would
require changes/additions to your current filters.*

Opinions/comments/experiences of how other lists handled this are welcome.

I've been reading this stuff for 4 days straight now and my brain hurts.
 Apologies if it's less than clear.

-- 
Terry