Hello,

the DMARC Mitigation action “Replace From: with list address” is evaluated in mailman/handlers/dmarc.py:munged_headers(). In the case, where From: is a non-member email address, without display part, which non-member may post, this happens:

realname = email realname = re.sub(r'@([^ .]+\.)+[^ .]+$', '---', realname) with _.using(mlist.preferred_language.code): via = _('${realname} via ${mlist.display_name}') display_name = str(Header(via, mlist.preferred_language.charset)) value = [('From', formataddr((display_name, mlist.posting_address)))]

In short, if a@b is a non-member, who may post to mailing list “E c@d”, and b is DMARC-protected, the final distrubuted email will have

From: "a--- via E c@d" Reply-To: a@b

compare to the IETF mailing lists, which would send: From: a=40b@d where a and b are from a@b, d is from c@d

The bottom of https://answers.uillinois.edu/illinois/page.php?id=86787 describes the mitigariton options offered by Sympa:

display name From: User Name listName@lists.illinois.edu

display name and e-mail From: “User Name” (userEmail@address.com) < listName@lists.illinois.edu >

email “via Mailing List” From: “User Name” (userEmail@address.com via listName Mailing List) listName@lists.illinois.edu

name “via Mailing List” From: “User Name” listName@lists.illinois.edu (the website likely means:) From: “User Name via listName” listName@lists.illinois.edu

As can be seen, the other MLMs do not replace domains with --- . I find ugly the --- , inserted by mailman. In my real-world case the From: is aaa@example.org, the ML name is aaa@l.example.org (localname is the same, the domains are different). The result is:

From: aaa--- via Aaa aaa@l.example.org

So there is twice trippe-A and @example.org disappeared. Mentioning twice AAA in the display name in this case really has to added value.

That said, I propose removing now the line

realname = re.sub(r'@([^ .]+\.)+[^ .]+$', '---', realname)

and in the future offer as options: From: User Name listName@lists.illinois.edu From: “User Name” (userEmail@address.com) < listName@lists.illinois.edu > From: “User Name” (userEmail@address.com via listName Mailing List) listName@lists.illinois.edu From: “User Name via listName” listName@lists.illinois.edu