[Mailman-Users] DMARC and Bellsouth, etc.

Stephen J. Turnbull stephen at xemacs.org
Wed Apr 16 20:11:35 CEST 2014

Jose I. Rojas  writes:

 > We have a community group mail list which we run using Mailman and
 > have lately had a problem getting our emails to members who have
 > Bellsouth and Yahoo email addresses. I've seen the posts about DMARC
 > but am not that tech-savvy to figure out what this means and how to
 > resolve.

What it means right now is that posts with "@yahoo.com" in the "From"
header field will not be delivered to users whose subscribed addresses
are at a long list of large email service providers.

If emails posted by users with "@gmail.com" and "@harvard.edu" etc
addresses are getting through to everybody, but emails from
"@yahoo.com" members are not, then the problem may very well be
Yahoo!'s DMARC policy.

 > Our ISP tells us domain is "RFC-compliant" and problem must be with
 > Bellsouth or Yahoo.

That's not very helpful of them.

 > How do we resolve this?  What is the fix?

If in fact the problem is Yahoo!'s DMARC policy, you can't resolve it
and there is no fix.  Simply put, Yahoo! does not permit their users
to post to modern mailing lists that conform to the mail standards.
There are four possible workarounds, depending on the access you have
to your mailing list's configuration:

(1) You can tell your members with @yahoo.com addresses to post from a
    different domain.  This is what I personally recommend, as it (a)
    conforms to Yahoo's stated policy and (b) makes Yahoo users
    unhappy with their provider, whose behavior is causing denial of
    service to thousands, perhaps millions, of mailing list users.

    My experience with this approach is "no complaints", but my users
    are unusual in that they don't really care about their yahoo.com
    addresses for various reasons.  People who do most or all of their
    mail using Yahoo addresses will find this painful.  Depending on
    how actively you want to protest Yahoo's behavior, you may or may
    not be willing to impose that pain.

(2) You can break your mailing lists by using the author_is_list
    option in Mailman 2.1.16 and later.  This option will only be
    available if the site configuration has ALLOW_AUTHOR_IS_LIST set
    to "Yes".  This will cause the list to replace the author's
    address with its own address in "From".  However, your domain may
    not permit this, as it's a clear violation of the mail RFCs.

(3) There is a patch to have Mailman encapsulate posts from yahoo.com
    addresses in a "one-message digest".  This is RFC-conformant, but
    some users may have difficulty reading such mail.  (Frequently
    reported on iPhones.)  It also requires using a third-party patch
    for Mailman, which may be prohibited by your ISP or beyond your
    technical capability in the short run.

(4) You can operate Mailman in pure pass-through mode.  I believe it
    is sufficient to configure Mailman to (a) have a completely empty
    header (not even whitespace) (b) a completely empty footer (c) no
    list prefix in the Subject header field.  This is conformant to
    the RFCs, but may place you in violation of anti-spam law (because
    for most users there will be no visible indication of how to
    unsubscribe from the list).

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