The mailing list for listmasters using Sympa

[Stephen Jarjoura <address@concealed>]

You can enable DMARC protection:

• DMARC Protection
• DMARC Protection Config Options

And, you can also re-sign outgoing email, via DKIM:

• DKIM and ARC: Setup Sympa
  
• DKIM/DMARC/ARC Config Options

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Stephen A. Jarjoura

Collaborative Services

On Wed, Nov 22, 2023 at 11:40 AM Mail administrator, Otto Makela <address@concealed> wrote:

I've been working with getting regular DKIM-signed messages to pass intact
through Sympa, and if you give up Subject tagging (custom_subject) it can
definitely be achieved for (some) senders.

Unfortunately, this depends in parts on how "wide" the DKIM signature is.
One prominent sender to our mailing lists uses signing that includes
everything imaginable, including List-Id. I've taken this as a hint they
don't want their people on any external mailing lists, and they're re-
thinking their choices with my threat of unsubscribing all their users.

However, another alternative (supported by eg Mailman, described by them
as "DMARC Munging") is to change mailing behavior rather radically,
by editing the outgoing mailing list message headers:

        From: "DISPLAY_NAME via LIST_NAME" <LIST_POSTING_ADDRESS>
        Reply-To: ORIGINAL_FROM_ADDRESS

And then signing the message with your own DKIM signature,
since of course the list posting address is signable by your server.

(I can see how messing with the DISPLAY_NAME will at some point cause
problems with Mac Mail and some other clients, which are greedy about
squirreling away and trying to merge together seen "From" addresses)

Mailman implements this here:
https://gitlab.com/mailman/mailman/-/blob/master/src/mailman/handlers/dmarc.py

Can (and should) similar functionality be added to Sympa?

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address@concealed (Mail Administrator, Otto J. Makela)