[Nottingham] [Maillist] 'Munging' the "From" mail headers on this list?

[Andy Smith]

Hi Jason,

On Mon, May 23, 2016 at 09:01:44AM +0100, Jason Irwin via Nottingham wrote:
> Majority rules and all that, but my vote is we go back to using
> people's email addresses again. Most of us seem to have them
> appearing in the "Reply-to" section anyhoo.

Note that that will mean that emails from DMARC-using people will be
rejected by DMARC-enforcing recipients (I imagine preventing this was
the reason that the admins of mailman.lug.org.uk made this change).

Aside from the "replace from address with list's address and add
reply-to" and the "do nothing to the from address or reply-to" there
are also some other options for what to do with emails from domains
with DMARC set.

Under
http://mailman.lug.org.uk/mailman/admin/nottingham/privacy/sender
the list admin will find the dmarc_moderation_setting option, which
will most likely currently be set to "Accept". The other valid
values for it are "Monge From", "Wrap Message", "Reject" and
"Discard". Here's the help text:

    dmarc_moderation_action (privacy): Action to take when anyone posts
    to the list from a domain with a DMARC Reject/Quarantine Policy.

        Munge From -- applies the from_is_list Munge From
        transformation to these messages.

        Wrap Message -- applies the from_is_list Wrap Message
        transformation to these messages.

        Reject -- this automatically rejects the message by sending
        a bounce notice to the post's author. The text of the bounce
        notice can be configured by you.

        Discard -- this simply discards the message, with no notice
        sent to the post's author. 

"Munge From" is what is currently being done to all messages. If
this is not desired then that could be turned off and it could be
done only for emails from people whose email providers enforce
DMARC.

The from_is_list setting can be found at
http://mailman.lug.org.uk/mailman/admin/nottingham/general and is
currently set to "Munge From". Its help text:

    from_is_list (general): Replace the From: header address with
    the list's posting address to mitigate issues stemming from the
    original From: domain's DMARC or similar policies.

    Several protocols now in wide use attempt to ensure that use of
    the domain in the author's address (ie, in the From: header
    field) is authorized by that domain. These protocols may be
    incompatible with common list features such as footers, causing
    participating email services to bounce list traffic merely
    because of the address in the From: field. This has resulted in
    members being unsubscribed despite being perfectly able to
    receive mail.

    The following actions are applied to all list messages when
    selected here. To apply these actions only to messages where the
    domain in the From: header is determined to use such a protocol,
    see the dmarc_moderation_action settings under Privacy
    options... -> Sender filters.

    Settings:

    No
            Do nothing special. This is appropriate for anonymous
            lists. It is appropriate for dedicated announcement
            lists, unless the From: address of authorized posters
            might be in a domain with a DMARC or similar policy. It
            is also appropriate if you choose to use
            dmarc_moderation_action other than Accept for this list.
    Munge From
            This action replaces the poster's address in the From:
            header with the list's posting address and adds the
            poster's address to the addresses in the original
            Reply-To: header.
    Wrap Message
            Just wrap the message in an outer message with the From:
            header containing the list's posting address and with
            the original From: address added to the addresses in the
            original Reply-To: header and with Content-Type:
            message/rfc822. This is effectively a one message MIME
            format digest.

    The transformations for anonymous_list are applied before any of
    these actions. It is not useful to apply actions other than No
    to an anonymous list, and if you do so, the result may be
    surprising.

    The Reply-To: header munging actions below interact with these actions as follows:

    first_strip_reply_to = Yes will remove all the incoming
    Reply-To: addresses but will still add the poster's address to
    Reply-To: for all three settings of reply_goes_to_list which
    respectively will result in just the poster's address, the
    poster's address and the list posting address or the poster's
    address and the explicit reply_to_address in the outgoing
    Reply-To: header. If first_strip_reply_to = No the poster's
    address in the original From: header, if not already included in
    the Reply-To:, will be added to any existing Reply-To:
    address(es).

    These actions, whether selected here or via
    dmarc_moderation_action, do not apply to messages in digests or
    archives or sent to usenet via the Mail<->News gateways.

    If dmarc_moderation_action applies to this message with an
    action other than Accept, that action rather than this is
    applied

Tricky stuff…

Cheers,
Andy

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