1 Aug
2021
1 Aug
'21
6:30 p.m.
Chris,
Yes it is a complicated situation, mailing list operators have often objected to
DMARC/DKIM/SPF because of this.
And, as you correctly describe, it also depends on the configuration of the mailing list.
I think in the current setup (mail is "From 44net(a)mailman.ampr.org") the correct
procedure is to
delete the DKIM-Signature header (after its validation on the incoming side which is
likely done by other software)
so that it does not appear in the outgoing mails from the list.
The receiving server sees the mailman.ampr.org sender so it has no reason to lookup the
DMARC policy
for the original sender, and there is no invalid DKIM signature so no problems with that
either.
The mailman people recognize that solution but I think it has not been implemented yet.
But maybe you have some other processing between the receiving mailserver and mailman
(like procmail)
where you could delete the header.
Rob
On 8/1/21 1:11 PM, Chris Smith via 44Net wrote:
Hi Rob,
Configuring a mailing list with regards to DMARC, SKIM/SPF is indeed a problem!
The issue stems from that fact that if someone sends an email from a domain that has a
published DMARC policy, and is DKIM signed, then in order for that DMARC policy to be
passed by the recipient, the From address, Subject and Body of the message must not be
altered, otherwise the DKIM signing fails.
The 44Net mailing list changes the Subject by pre-pending "[44net]”, it also alters
the body by appending the list information block of text. So right away DKIM will always
fail.
The mailman authors added an option to get around this by munging the From address
header. So if I send an email from: chris(a)ardc.net this gets changed to:
44net(a)mailman.ampr.org <mailto:44net@mailman.ampr.org>
My address gets added on as a CC: field (unless I specifically switch that off in my
personal settings) so generally you can see who originally sent the email, which gives you
the option to reply direct if you wish to.
However, there are better ways of doing this, without “munging” headers that are not
supposed to get touched, like the From header, which was designed to never change as it
identifies the original source of the email. One way of doing this would be to leave the
From, Subject and Body alone and instead add a Sender header with the
44net(a)mailman.ampr.org <mailto:44net@mailman.ampr.org> address in. The Sender header
was designed to identify someone sending an email on behalf of someone else, which is
effectively what a mailing list is doing.
TBH, I haven’t touched the mailing list server (except to keep it updated) since Brian
set it up. How Brian set it up was the best option at the time, but things change,
technology moves on, often quite quickly in the internet world!
The munging of the From header does generally work, although, as you correctly pointed
out, it does cause issues with recipients that check DMARC policies and DKIM signatures.
Also, the mailing list server has never been setup to sign outgoing emails, there is an
SPF record in place, but no DKIM for the mailing list server. We do have DMARC, DKIM &
SPF for the top domain ampr.org <http://ampr.org/> and all outgoing mails from
@ampr.org will be signed and there should be alignment with DKIM and SPF, but we could
never apply a policy to subdomains of ampr.org <http://ampr.org/> as all the
membership use it, e.g. I can setup chris(a)g1fef.ampr.org
<mailto:chris@g1fef.ampr.org> etc. As the mailing list server uses a subdomain:
mailman.ampr.org <http://mailman.ampr.org/> this also created a problem.
This is one of the reasons ARDC moved to @ardc.net for emails, as we can fully control
the domain without worrying about subdomains. Even though there is a mechanism for setting
the policy on the top domain and subdomains separately, a lot of MTA’s still don’t honour
these and we got an awful lot of issues with email deliverability when we used @ampr.org
now we are on @ardc.net the problems have mostly gone away.
Perhaps we should move the mailing list to ardc.net <http://ardc.net/> and set it
up to interact better with today’s email environment? Just a thought.
Chris - G1FEF
On 1 Aug 2021, at 10:30, Rob PE1CHL via 44Net
<44net(a)mailman.ampr.org> wrote:
I think one reason for bounces could be that the mailman mailing list does not handle
DKIM properly.
When a user sends a mail to the list, it passes through the DKIM signature, but it also
modifies the mail
(adding a standard footer as the mimimum, probably more)
As a result, the DKIM signature of messages received via the list is invalid, and maybe
some
mail servers see it as a reason to reject the mail (as if it is spoofed). In my mail
system, most
mails in this list get a red color because that is what some rule processing here does to
get my
attention to falsified mails.
In fact this should be solved by mailman, but some googling seems to indicate that the
mailman
people know that, but have not yet come into action. So likely there is no setting in
the admin
panel to easily solve this. Maybe some extra software or feature of the existing
software could
be used to work around this. That would at the minimum have to delete any
DKIM-Signature:
header on incoming mail (unfortunately this is a multiline header so it will require more
than passing
through some simple grep or sed), and additionally it could add a new DKIM signature afer
all
mailman processing, for the mailman.ampr.org domain. But the latter is optional.
Rob
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