[Mailman-Users] options for dealing with DMARC

Jordan Brown mailman at jordan.maileater.net
Thu Dec 28 14:57:31 EST 2017

I've been running my mailing list for a few years with "Munge From" to
defend against DMARC rejection.  This means that my messages get

    From: Joe User <mymailinglist at mydomain.com>
    Reply-To: Joe User <joe at example.com>

That mostly works, but sometimes confuses people a bit, and just now
I've had somebody send what I think was intended as a private address to
that From line, not to the Reply-To line.  (I think their e-mail client,
Pegasus, has an excessively flexible policy on which headers to use for
a reply and may be subtly misconfigured, but maybe they just naively
copied the From line.)

That's leading me to wonder whether there's another way, whether I can
leave From alone and still get past the DMARC checks.  Wikipedia tells
me that DMARC passes if either SPF *or* DKIM passes.  There's no hope
for SPF with the original sender in From, because the mailing list
server isn't the user's mail server.  However, DKIM seems like it
*might* pass, if I'm careful in how I configure the mailing list.  In
particular, it looks like I'd have to get rid of the message footer. 
That would be OK.  Looks like I might also have to kill off the
[ListName] addition to the Subject, which is less OK but might be better
than the alternative.

Before I go recruit a couple of users from several DMARC-using providers
and run some tests, can anybody tell me if there is any hope there, and
maybe share some configuration tips?

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