DMARC policy, list messages sent to spam, and mailing list changes to deal with it

Hello, loyal subscribers and users,

This is an announcement about the list itself; sorry for the noise.

As you have gathered from various discussions on the list, the use and
enforcement of DMARC policy by the large email providers has made life for
mailing list administrators hell.  Messages to mailing lists coming from
domains with restrictive DMARC policies ("quarantine" or "reject") end up
getting refused while the list manager tries to deliver them to the Gmails and
Yahoos and other big players.

There isn't an ideal solution to this problem.  DMARC has been known since its
inception to be incompatible with normal mailing-list mechanisms, but the big
players don't care.  Frankly, I don't think they want mailing lists to exist
anymore.

But something had to change.  Deliverability of list messages has gotten
terrible.  So I've implemented a mechanism for the getmail list to work around
the problem.

Here's how this may affect you.  If the address you subscribe to the list with
belongs to a domain with a restrictive DMARC policy published in DNS, then the
mailing list manager will modify -- munge -- the From: header field in your
message, so that it no longer points to that domain.  Your original address
will still show up, in the "display name" portion of that address, like this:

  From: "Joe <[email protected]>" <[email protected]>

So your original address is still visible in the informational-only
display-name portion of From: header, but the actual address is one in the
mailing list's domain, to avoid triggering DMARC rejections.  This is
necessary because DMARC is defined to work on the From: header contents, and
nothing else.

The list manager will also copy your original From: header field contents into
a new Sender: header field.

The biggest effect this will have is if a list subscriber decides to reply
directly to you from a list message, his or her MUA is probably going to
default to sending it to this "mask address".  The list manager will bounce it
with a helpful message explaining the situation.  The Sender: field hack is
the best I can do to try to avoid this problem.

Action for your part: if you know you're in a domain with a restrictive DMARC
policy, and you want to avoid private replies being affected like this,
configure your MUA to add a Reply-to: header field containing your address.
This isn't ideal either; it can cause list reply messages which the authors
intended to go to the list to instead go directly to you, but there's not much
to do about that.

You can check your domain's DMARC policy by entering it into this tool:
https://mxtoolbox.com/SuperTool.aspx?action=dmarc:

If the result shows the "p" tag contains "quarantine" or "reject", your domain
is affected.


I realize this is complicated.  I'm happy to discuss this further with anyone
who wants to know more.

Please let me know if you notice any problems with the list under this new
configuration.

Charles
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Charles Cazabon
GPL'ed software available at:               http://pyropus.ca/software/
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