[Mailman-Users] DMARC and Reply-To lines with from_is_list munging.

Lindsay Haisley fmouse at fmp.com
Fri May 9 18:08:07 CEST 2014

On Thu, 2014-05-08 at 15:42 -0400, Glenn Sieb wrote:
> If I felt what my users were asking for was unreasonable, I wouldn't
> have bothered to bring it here. They'd *like* to see who's posting so if
> they *choose* to reply privately they can. In the past, this was easy
> enough. The From: line was there with the OP's email address. Now, as
> far as I can tell, depending on the MUA the *poster* uses, there *might*
> be two Reply-Tos--one with the OP email, one with the list address. But
> that's not reliable, as it doesn't happen for ALL posters.
> Hell, even a munged From: like:
> "ges+lists at wingfoot dot org via Mailman-Users
> <mailman-users at python.org>"
> would be a vast improvement over:
> "ges+lists--- via Mailman-Users <mailman-users at python.org>"

I'm not as knowledgeable as Stephen or Mark, but I've been working with
Internet email since the early 90s or so and have read the founding
RFCs.  One of the principles underlying the design of the Internet email
system is that information should never be intentionally abandoned.
Nothing gets dumped into the cosmic bit bucket, neither header
information nor content, and NDRs and DSNs keep the sender appraised of
problems with delivery.  This has been a strong argument against munging
of Reply-To headers going back quite a few years.  Information may be
_added_ by a component in the delivery chain (and generally is) but not

Arguably, the correct response to DMARC filtering _should_ be the MIME
encapsulation of list mail, with appropriate RFC 2369 headers added to
the enclosing MIME structure leaving the content un-munged, with all
information from the original poster intact.  Arguably, MUAs should be
transparent to this.  Arguably, this would have been the best design for
the operation of mailing lists in email-space from the git-go.

We're stuck in the Real World, however, where Apple and probably other
MUA authors and designers have cut corners in design and we're forced
into a corner where information loss of some sort is imposed on us.
From: header munging is decidedly ugly!  It's perhaps the least ugly
solution that still works reliably to deliver content to _everyone_ even
though the information loss limits choice on the receiving end.

Your suggested partial solution ("ges+lists at wingfoot dot org via
Mailman-Users ...") is also ugly, but given the situation we're in at
this point, IMHO it has merit and should be worth some consideration in
the design of Mailman.  What goes into an address comment is, or should
be, purely informational on a human level, and ignored on a
computational level.  Whether or not it would would confuse people is
another matter.  It ain't the kinder, gentler Internet I jumped into
back in 1994!

Lindsay Haisley       | "Everything works if you let it"
FMP Computer Services |
512-259-1190          |     - The Roadie
http://www.fmp.com    |

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