[CentOS] Some subscribers posts to the list ending up in Gmail spam

Sun Apr 5 01:35:45 UTC 2015
Nataraj <incoming-centos at rjl.com>

On 04/04/2015 09:59 AM, Andrew Holway wrote:
> Did we work out the technical reason why some users that post to the list
> are getting dumped into gmail spam?
>
> Ta,
>
> Andrew
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> http://lists.centos.org/mailman/listinfo/centos

It is most probably due to the various issues around dmarc, dkim and
mailing list servers for which there is currently no great solution to
the problem.  If, for example I look at the your message (in this case,
the one I am responding to), I see the following:

 1. The message has intact a dkim signature from gmail, so the Centos
    mailman server is not stripping the dkim sig from the original
    sender, which recent versions of mailman can be configured to do.
 2. The CentOS mailman server adds its own footer, changing the checksum
    of the message, so the dkim signature is no longer valid, therefore
    when any receiving mail server checks the DKIM sig it fails as it
    did with my own mailserver.
 3. The centos server does NOT add its own DKIM sig and appears to have
    no DMARC record in the DNS (dig txt _dmarc.centos.org.)  These are
    not necessarily a good idea anyway for mail coming from a mailing
    list server because in order to add a DKIM sig the from of the
    message would have to be changed to name at centos.org since the
    mailman server can't itself sign for a sender from another domain.

I'm not suggesting that DKIM or DMARC are a good solution to anything,
however several of the FREEMAIL providers do pay attention to these
things, so the CentOS mailserver admin might want to consider having
mailman strip existing DKIM sig's from the mail (or alternatively not
adding a footer).  You can check the mailman doc/mailing list for other
relevent options for working around these problems.

.  I believe that if, in your gmail account, you keep marking as "NOT
SPAM" any false positives it will send more of these messages to the
right folder.

There has been an abundance of discussions in the past about these
issues on the various mailman, dmarc and dkim mailing lists as well as
in many other places.  This whole issue hit the fan early in 2014 when
yahoo and aol changed their DMARC policy to reject incoming mail that
failed the DMARC test.  Gmail, however, does not enforce the "reject" in
others DMARC policy, but instead sends the email to the spambox (gmail
also may send email to the spambox if it has no DKIM signature at all). 
I found that when I added (valid) DKIM signatures and a DMARC record for
my domains, recipient freemail users messages started going to their
inbox instead of their spambox.

Nataraj