*HCS* Final Call for Ignitaries!

Brendan Connell bdconnel at fas.harvard.edu
Mon Oct 2 14:31:40 EDT 2000

On Mon, 2 Oct 2000, britt wrote:

> uh, no it's not broken.

<reels in bait>

Oh, yes it is.  Admittedly, this is the subject of numerous flamewars...
but munging the Reply-to: line really IS a Bad Idea (TM).  If you're not
convinced, here's one of the best cases I've seen made against it...



                    ``Reply-To'' Munging Considered Harmful
An Earnest Plea to Mailing List Administrators
   An email message requires some amount of processing when it is
   redistributed to a mailing list. At the very least, the envelope must
   be rewritten to redirect bounces directly to the list administrator.
   While the message is being processed, the list administrator might
   take advantage of the opportunity to munge some of the message
   Some forms of header munging are helpful, such as special
   loop-detection headers. Others are questionable. Most are ill-advised
   or dangerous. Many list adminstrators want to add a Reply-To header
   that points back to the list. This transformation also is one of the
   most ill-advised.
   Some administrators claim that Reply-To munging makes it easier for
   users to respond to the entire list, and helps encourage list traffic.
   These benefits are fallacious. Moreover, Reply-To can have harmful --
   even dangerous -- effects. If you think Reply-To munging is a good
   idea, I hope I can change your mind.
The Principle of Minimal Munging

   Email processing is pretty tricky. Read through RFC-822, the Standard
   for the Format of ARPA Internet Text Messages, sometime. It is 47
   pages of dense, dry detail. A lot of engineering and consideration
   went into this work. Even still, RFC-822 leaves many corner conditions
   and specialized circumstances poorly specified. RFC-1123, the
   commonly-called Internet Host Requirements document, adds a couple
   dozen more pages, and remedies some of the defects. Then there is
   MIME, X.400 mapping, and a handful of other standards and conventions
   -- some documented and some folklore. Email handling is surprisingly
   complicated, and even an innocuous-sounding change might have grave,
   unintended consequences.
   The ``Principle of Minimal Munging'' is a good rule that will keep you
   out of trouble. It says you should not make any changes to an email
   header unless you know precisely what you want to do, why you want to
   do it, and what it will affect. Unless you can articulate a clear
   reason for munging and understand the full consequences of the action,
   you should not do it.
   The ``Principle of Minimal Munging'' will help you avoid the sorts of
   problems we are about to discuss. This principle is a rule designed to
   be broken, but you can avoid some significant heartache by thinking
   hard and long before you do so.
It Adds Nothing

   Reply-To munging does not benefit the user with a reasonable mailer.
   People want to munge Reply-To headers to make ``reply back to the
   list'' easy. But it already is easy. Reasonable mail programs have two
   separate ``reply'' commands: one that replies directly to the author
   of a message, and another that replies to the author plus all of the
   list recipients. Even the lowly Berkeley Mail command has had this for
   about a decade.
   Any reasonable, modern mailer provides this feature. I prefer the Elm
   mailer. It has separate ``r)eply'' and ``g)roup-reply'' commands. If I
   want to reply to the author of a message, I strike the ``r'' key. If I
   want to send a reply to the entire list, I hit ``g'' instead. Piece 'o
   I mention Elm here (and a lot later on) simply because that's the
   mailer I use everyday. This sort of support is not unique to Elm Any
   reasonable mailer provides it. The Pine mailer, for instance, asks
   directly, ``Reply to all recipients?'' when you use the ``r'' command.
   It doesn't get much easier than that!
   Whichever mailer you choose, please read the fine manual that comes
   with it. Unless you are stuck with some decrepit mail system, I bet
   you'll find it has a similar feature. If so, you easily can choose to
   direct your responses either to the original author or the entire
   list. Mauling the mail headers doesn't make it any easier.
It Makes Things Break

   If you use a reasonable mailer, Reply-To munging does not provide any
   new functionality. It, in fact, decreases functionality. Reply-To
   munging destroys the ``reply-to-author'' capability. Munging makes
   this command act effectively the same as the ``reply-to-group''
   function. We haven't added anything new, we've only taken away.
   Reply-To munging is not merely benign, it is harmful. It renders a
   useful mail capability inoperative.
Freedom of Choice

   Some administrators justify Reply-To munging by saying, ``All
   responses should go directly to the list anyway.'' This is arrogant.
   You should allow me to decide exactly how I wish to respond to a
   message. If I feel a public response is justified, I'll hit the ``g''
   key and tell Elm to do a group-reply. If I believe a private response
   is more appropriate, I'll use ``r'' to send one. Please allow me the
   freedom to decide how to handle a message.
Can't Find My Way Back Home

   It may be impossible to reply to the author of a message once the
   Reply-To header is munged. The Reply-To header was not invented on a
   whim. It is there for the sender of a mail message to use. If you
   stomp on this header, you can lose important information.
   There are good reasons why the sender might insert a Reply-To header.
   The sender might not be the original author of the message (the name
   that appears in the From header). If responses should return to the
   sender and not the original author, then the sender will insert a
   Reply-To header. Or, maybe the sender added a Reply-To because he or
   she cannot receive email at the account from which the message was
   sent. There are many good reasons to place a Reply-To header into a
   mailing list message.
   If the Reply-To is munged by the mailing list, the value provided by
   the original sender is lost. Reply-To munging can make it impossible
   to reach the sender of a message.
Coddling the Brain-Dead, Penalizing the Conscientious

   There are, unfortunately, poorly implemented mail programs that lack
   separate reply-to-author and reply-to-group functions. A user saddled
   with such a brain-dead mailer can benefit from Reply-To munging. It
   makes it easier for him or her to send responses directly to the list.
   This change, however, penalizes the conscientious person that uses a
   reasonable mailer. This is a poor trade-off. As Internet list
   administrators, we should encourage people to run reasonable software.
   If a few people need to type in a full reply address so that everybody
   else can use all the features of their mailer, I say, ``Fine!'' We
   should not penalize the conscientious to coddle those who run
   brain-dead software.
Principle of Least Work

   Compare and contrast: the work required for me (or any other Elm user)
   to reply on lists that do and don't employ Reply-To munging.
                Case One:               Case Two:
Action          Without Munging         With Munging
=============   =====================   =====================

Reply to        Hit the "g"             Probably hit the "r"
everybody.      key.                    key, but maybe the "g"
                                        key if there were other
                                        recipients of the message.

Reply just      Hit the "r"             Look at the original
to author.      key.                    message header, write
                                        down the sender's
                                        email address, hit the
                                        "r" key, call up the
                                        header editing menu,
                                        erase the current To:
                                        value, and type in the
                                        sender's full email
                                        address.  And pray the
                                        correct address wasn't
                                        wiped out when the Reply-To
                                        was munged.

   Again, your preferred mailer probably implements this feature in a
   different fashion. Nonetheless, it should be easy. I'll take box
   number one, Monte.
Principle of Least Surprise

   When I hit the ``r'' key in Elm, it sends a response to the author of
   a message. When you munge the Reply-To header you change this action
   so that it does something entirely different from what I expect. This
   creates specialized behavior for your mailing list, which increases
   the potential for surprise. I'm not schooled in the science of human
   factors, but I suspect surprise is not an element of a robust user
   Private messages frequently are broadcast across lists that do
   Reply-To munging. That's an empirical fact. It's what happens when you
   violate the principle of least surprise.
Principle of Least Damage

   Consider the damage when things go awry. If you do not munge the
   Reply-To header and a list subscriber accidentally sends a response
   via private email instead of to the list, he or she has to follow up
   with a message that says, ``Ooops! I meant to send that to the list.
   Could you please forward a copy for me.'' That's a hassle, and it
   happens from time to time.
   What happens, however, when a person mistakenly broadcasts a private
   message to the entire list? If the message is a complaint about the
   personal hygiene of sender's boss, or the sex life of his or her
   roommate, a simple ``Ooops!'' won't cut it. About all you can do is
   send a followup with lots of retroactive smileys (weak). Or say your
   cat was dancing on the keyboard (better). Or start reading the
   classifieds for a new job/roommate/set of teeth (most likely).
   Reply-To munging encourages catastrophic failure modes. Sure, you
   don't need Reply-To munging to create this sort of damage. A simple
   slip of the fingers will suffice. When, however, you violate the
   ``Principle of Least Surprise'' you invite this sort of disaster. A
   responsible list administrator will avoid creating avenues that lead
   to such extreme damage.
And in the End...

   If you are not convinced yet, then allow me one final plea. I
   contribute to the Elm mailer development team. I get to see a lot of
   the wants and requests from the user community. Guess what feature
   more and more people are asking for? A third reply command -- one that
   ignores any existing Reply-To header! Want to guess why people are
   asking for it? If you think you are doing your subscribers a service
   by munging Reply-To headers, you are kidding yourself. You are making
   your subscribers miserable.
   Some list administrators, even after reading all this, seem to say,
   ``Oh, it's not that bad. Besides, my subscribers like it!'' If they
   do, it's probably because they haven't bothered to learn to use the
   ``reply-to-group'' feature of their mailer. Instead of going through
   all the trouble of making your list gateway scribble on email headers,
   how about making an effort to educate your subscribers?

   Many people want to munge Reply-To headers. They believe it makes
   reply-to-list easier, and it encourages more list traffic. It really
   does neither, and is a very poor idea. Reply-To munging suffers from
   the following problems:
     * It violates the principle of minimal munging.
     * It provides no benefit to the user of a reasonable mailer.
     * It limits a subscriber's freedom to choose how he or she will
       direct a response.
     * It actually reduces functionality for the user of a reasonable
     * It removes important information, which can make it impossible to
       get back to the message sender.
     * It penalizes the person with a reasonable mailer in order to
       coddle those running brain-dead software.
     * It violates the principle of least work because complicates the
       procedure for replying to messages.
     * It violates the principle of least surprise because it changes the
       way a mailer works.
     * It violates the principle of least damage, and it encourages a
       failure mode that can be extremely embarrassing -- or worse.
     * Your subscribers don't want you to do it. Or, at least the ones
       who have bothered to read the docs for their mailer don't want you
       to do it.

   In case you are wondering, yes, I once thought Reply-To munging was a
   nifty idea. I got better though.
   When I started running email lists, I munged 'em all. One day I
   accidentally sent a private, personal reply out over one of my own
   damn lists. If the list owner can't remember how to use the list
   properly, no way will the subscribers be able to sort it out. I
   stopped munging the very next day.
   On the whole, it has worked out quite well. Yes, on occasion somebody
   mistakenly responds directly to the author of a message when they
   wanted to reply to the group. Most folks, however, seem to catch on
   pretty fast to how it works, and seem to appreciate the flexibility.
   Moreover, private responses mistakenly sent to the entire list have
   become an almost unheard-of event.
What do You Think?

   Leave your comments and see what others say in the discussion forum.
    Chip Rosenthal
    <chip at unicom.com>
   Back to the Paperware Archive.
   Up to Unicom Systems home page.
   Let us know your comments, corrections, additions, suggestions.
$Id: reply-to-harmful.html,v 1.17 1999/01/05 09:08:03 chip Exp $
$Log: reply-to-harmful.html,v $
# Revision 1.17  1999/01/05  09:08:03  chip
# fixed links to RFCs
# started logging modification history

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