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327 lines
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<!-- $Id: reply-to-harmful.html,v 1.20 2002/11/15 03:46:04 chip Exp $ -->
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<TITLE>"Reply-To" Munging Considered Harmful</TITLE>
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<BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#5500EE" ALINK="#FF0000" VLINK="#551A8B">
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<h1>This Page is a Mirror</h1>
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<p>This page has been mirrored for historical preservation</p>
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<hr>
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<H1>"Reply-To" Munging Considered Harmful</H1>
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<H2>An Earnest Plea to Mailing List Administrators</H2>
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<HR>
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<P>An email message requires some amount of processing when it is
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redistributed to a mailing list. At the very least, the envelope must
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be rewritten to redirect bounces directly to the list administrator.
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While the message is being processed, the list administrator might
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take advantage of the opportunity to
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<A HREF="http://www.fwi.uva.nl/~mes/jargon/m/munge.html">munge</A> some
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of the message headers.
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<P>Some forms of header munging are helpful, such as special loop-detection
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headers. Others are questionable. Most are ill-advised or dangerous.
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Many list adminstrators want to add a <KBD>Reply-To</KBD> header that
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points back to the list. This transformation also is one of the most
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ill-advised.
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<P>Some administrators claim that <KBD>Reply-To</KBD> munging makes
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it easier for users to respond to the entire list, and helps encourage
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list traffic. These benefits are fallacious. Moreover, <KBD>Reply-To</KBD>
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can have harmful -- even dangerous -- effects. If you think
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<KBD>Reply-To</KBD> munging is a good idea, I hope I can change your
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mind.
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<H2>The Principle of Minimal Munging</H2>
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<P>Email processing is pretty tricky. Read through
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<A HREF="ftp://ftp.isi.edu/in-notes/rfc822.txt">RFC-822</A>, the
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<CITE>Standard for the Format of ARPA Internet Text Messages</CITE>,
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sometime. It is 47 pages of dense, dry detail. A lot of engineering
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and consideration went into this work. Even still, RFC-822 leaves
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many corner conditions and specialized circumstances poorly specified.
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<A HREF="ftp://ftp.isi.edu/in-notes/rfc1123.txt">RFC-1123</A>, the
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commonly-called <CITE>Internet Host Requirements</CITE> document, adds
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a couple dozen more pages, and remedies some of the defects. Then
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there is MIME, X.400 mapping, and a handful of other standards and
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conventions -- some documented and some folklore. Email handling is
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surprisingly complicated, and even an innocuous-sounding change might
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have grave, unintended consequences.<P>
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<P>The "Principle of Minimal Munging" is a good rule that will keep
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you out of trouble. It says you should <EM>not</EM> make any changes
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to an email header unless you know precisely what you want to do,
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why you want to do it, and what it will affect. Unless you can
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articulate a clear reason for munging and understand the full consequences
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of the action, you should not do it.
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<P>The "Principle of Minimal Munging" will help you avoid the sorts of
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problems we are about to discuss. This principle <EM>is</EM> a rule
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designed to be broken, but you can avoid some significant heartache
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by thinking hard and long before you do so.
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<H2>It Adds Nothing</H2>
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<P><KBD>Reply-To</KBD> munging does not benefit the user with a reasonable
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mailer. People want to munge <KBD>Reply-To</KBD> headers to make
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"reply back to the list" easy. But it already is easy. Reasonable
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mail programs have two separate "reply" commands: one that replies
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directly to the author of a message, and another that replies to the
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author plus all of the list recipients. Even the lowly
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<A HREF="http://www.bsdi.com/bsdi-man/?Mail%281%29">Berkeley
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<CITE>Mail</CITE></A> command has had this for about a decade.
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<P>Any reasonable, modern mailer provides this feature. I prefer the
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<A HREF="http://www.myxa.com/myxa/elm.html"><CITE>Elm</CITE> mailer</A>.
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It has separate "r)eply" and "g)roup-reply" commands. If I
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want to reply to the author of a message, I strike the "<KBD>r</KBD>"
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key. If I want to send a reply to the entire list, I hit "<KBD>g</KBD>"
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instead. Piece 'o cake.
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<P>I mention <CITE>Elm</CITE> here (and a lot later on) simply because
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that's the mailer I use everyday. This sort of support is not unique
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to <CITE>Elm</CITE> Any reasonable mailer provides it. The
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<CITE>Pine</CITE> mailer, for instance, asks directly, "Reply to all
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recipients?" when you use the "<KBD>r</KBD>" command. It doesn't
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get much easier than that!
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<P>Whichever mailer you choose, please <EM>read</EM> the fine manual
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that comes with it. Unless you are stuck with some decrepit mail
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system, I bet you'll find it has a similar feature. If so, you easily
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can choose to direct your responses either to the original author or
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the entire list. Mauling the mail headers doesn't make it any easier.
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<H2>It Makes Things Break</H2>
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<P>If you use a reasonable mailer, <KBD>Reply-To</KBD> munging does not
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provide any new functionality. It, in fact, <EM>decreases</EM>
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functionality. <KBD>Reply-To</KBD> munging destroys the "reply-to-author"
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capability. Munging makes this command act effectively the same as
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the "reply-to-group" function. We haven't added anything new, we've
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only taken away. <KBD>Reply-To</KBD> munging is not merely benign,
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it is harmful. It renders a useful mail capability inoperative.
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<H2>Freedom of Choice</H2>
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<P>Some administrators justify <KBD>Reply-To</KBD> munging by saying,
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"All responses should go directly to the list anyway." This is
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arrogant. You should allow <EM>me</EM> to decide exactly how I wish
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to respond to a message. If I feel a public response is justified,
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I'll hit the "<KBD>g</KBD>" key and tell <CITE>Elm</CITE> to do a
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group-reply. If I believe a private response is more appropriate,
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I'll use "<KBD>r</KBD>" to send one. Please allow me the freedom
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to decide how to handle a message.
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<H2>Can't Find My Way Back Home</H2>
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<P>It may be impossible to reply to the author of a message once the
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<KBD>Reply-To</KBD> header is munged. The <KBD>Reply-To</KBD> header
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was not invented on a whim. It is there for the sender of a mail
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message to use. If you stomp on this header, you can lose important
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information.
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<P>There are good reasons why the sender might insert a <KBD>Reply-To</KBD>
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header. The sender might <EM>not</EM> be the original author of the
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message (the name that appears in the <KBD>From</KBD> header). If
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responses should return to the sender and not the original author,
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then the sender will insert a <KBD>Reply-To</KBD> header. Or, maybe
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the sender added a <KBD>Reply-To</KBD> because he or she cannot receive
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email at the account from which the message was sent. There are many
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good reasons to place a <KBD>Reply-To</KBD> header into a mailing list
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message.
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<P>If the <KBD>Reply-To</KBD> is munged by the mailing list, the value
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provided by the original sender is lost. <KBD>Reply-To</KBD> munging
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can make it impossible to reach the sender of a message.
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<H2>Coddling the Brain-Dead, Penalizing the Conscientious</H2>
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<P>There are, unfortunately, poorly implemented mail programs that lack
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separate reply-to-author and reply-to-group functions. A user saddled
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with such a brain-dead mailer can benefit from <KBD>Reply-To</KBD>
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munging. It makes it easier for him or her to send responses directly
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to the list.
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<P>This change, however, penalizes the conscientious person that uses
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a reasonable mailer. This is a poor trade-off. As Internet list
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administrators, we should encourage people to run reasonable software.
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If a few people need to type in a full reply address so that everybody
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else can use all the features of their mailer, I say, "Fine!" We
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should not penalize the conscientious to coddle those who run brain-dead
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software.
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<H2>Principle of Least Work</H2>
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<P>Compare and contrast: the work required for me (or any other
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<CITE>Elm</CITE> user) to reply on lists that do and don't employ
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<KBD>Reply-To</KBD> munging.
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<BLOCKQUOTE>
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<PRE>
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Case One: Case Two:
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Action Without Munging With Munging
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============= ===================== =====================
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Reply to Hit the "g" Probably hit the "r"
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everybody. key. key, but maybe the "g"
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key if there were other
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recipients of the message.
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Reply just Hit the "r" Look at the original
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to author. key. message header, write
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down the sender's
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email address, hit the
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"r" key, call up the
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header editing menu,
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erase the current To:
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value, and type in the
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sender's full email
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address. And pray the
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correct address wasn't
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wiped out when the Reply-To
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was munged.
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</PRE>
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</BLOCKQUOTE>
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<P>Again, your preferred mailer probably implements this feature in
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a different fashion. Nonetheless, it should be easy. I'll take box
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number one, Monte.
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<H2>Principle of Least Surprise</H2>
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<P>When I hit the "<KBD>r</KBD>" key in <CITE>Elm</CITE>, it sends a
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response to the author of a message. When you munge the <KBD>Reply-To</KBD>
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header you change this action so that it does something entirely
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different from what I expect. This creates specialized behavior for
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your mailing list, which increases the potential for surprise. I'm
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not schooled in the science of human factors, but I suspect surprise
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is not an element of a robust user interface.
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<P>Private messages frequently are broadcast across lists that do
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<KBD>Reply-To</KBD> munging. That's an empirical fact. It's what
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happens when you violate the principle of least surprise.
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<H2>Principle of Least Damage</H2>
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<P>Consider the damage when things go awry. If you do not munge the
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<CITE>Reply-To</CITE> header and a list subscriber accidentally sends a
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response via private email instead of to the list, he or she has to
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follow up with a message that says, "Ooops! I meant to send that to
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the list. Could you please forward a copy for me." That's a hassle,
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and it happens from time to time.
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<P>What happens, however, when a person mistakenly broadcasts a private
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message to the entire list? If the message is a complaint about the
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personal hygiene of sender's boss, or the sex life of his or her
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roommate, a simple "Ooops!" won't cut it. About all you can do is
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send a followup with lots of retroactive smileys (weak). Or say your
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cat was dancing on the keyboard (better). Or start reading the
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classifieds for a new job/roommate/set of teeth (most likely).
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<P><KBD>Reply-To</KBD> munging encourages catastrophic failure modes.
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Sure, you don't need <KBD>Reply-To</KBD> munging to create this sort
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of damage. A simple slip of the fingers will suffice. When, however,
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you violate the "Principle of Least Surprise" you invite this sort
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of disaster. A responsible list administrator will avoid creating
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avenues that lead to such extreme damage.
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<H2>And in the End...</H2>
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<P>If you are not convinced yet, then allow me one final plea. I contribute
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to the <CITE>Elm</CITE> mailer development team. I get to see a lot
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of the wants and requests from the user community. Guess what feature
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more and more people are asking for? A <EM>third</EM> reply command
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-- one that ignores any existing <KBD>Reply-To</KBD> header! Want to
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guess why people are asking for it? If you think you are doing your
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subscribers a service by munging <KBD>Reply-To</KBD> headers, you are
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kidding yourself. You are making your subscribers miserable.
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<P>Some list administrators, even after reading all this, seem to say,
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"Oh, it's not that bad. Besides, my subscribers like it!" If they
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do, it's probably because they haven't bothered to learn to use the
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"reply-to-group" feature of their mailer. Instead of going through
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all the trouble of making your list gateway scribble on email headers,
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how about making an effort to educate your subscribers?
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<H2>Summary</H2>
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<P>Many people want to munge <KBD>Reply-To</KBD> headers. They believe
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it makes reply-to-list easier, and it encourages more list traffic.
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It really does neither, and is a very poor idea. <KBD>Reply-To</KBD>
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munging suffers from the following problems:
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<UL>
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<LI>It violates the principle of minimal munging.
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<LI>It provides no benefit to the user of a reasonable mailer.
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<LI>It limits a subscriber's freedom to choose how he or she will direct
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a response.
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<LI>It actually reduces functionality for the user of a reasonable mailer.
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<LI>It removes important information, which can make it impossible to
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get back to the message sender.
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<LI>It penalizes the person with a reasonable mailer in order to coddle
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those running brain-dead software.
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<LI>It violates the principle of least work because complicates the
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procedure for replying to messages.
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<LI>It violates the principle of least surprise because it changes the
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way a mailer works.
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<LI>It violates the principle of least damage, and it encourages a failure
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mode that can be extremely embarrassing -- or worse.
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<LI>Your subscribers don't want you to do it. Or, at least the ones who
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have bothered to read the docs for their mailer don't want
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you to do it.
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</UL>
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<H2>Addendum</H2>
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<P>In case you are wondering, yes, I once thought <KBD>Reply-To</KBD> munging
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was a nifty idea. I got better though.
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<P>When I started running email lists, I munged 'em all. One day I
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accidentally sent a private, personal reply out over one of my own
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damn lists. If the list owner can't remember how to use the list
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properly, no way will the subscribers be able to sort it out. I
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stopped munging the very next day.
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<P>On the whole, it has worked out quite well. Yes, on occasion
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somebody mistakenly responds directly to the author of a message when
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they wanted to reply to the group. Most folks, however, seem to catch
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on pretty fast to how it works, and seem to appreciate the flexibility.
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Moreover, private responses mistakenly sent to the entire list have
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become an almost unheard-of event.
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<P>
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<HR>
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<ADDRESS>
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<A HREF="../people/chip/index.html">Chip Rosenthal</A><BR>
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<chip@unicom.com><BR>
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</ADDRESS>
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<P>
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<IMG SRC="../graphics/small-back.gif" ALIGN="top" ALT="" WIDTH="16" HEIGHT="16">
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<BR>
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<IMG SRC="../graphics/small-comment.gif" ALIGN="top" ALT="" WIDTH="16" HEIGHT="16">
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<A HREF="/misc/cmntform.html">Let us know</A>
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your comments, corrections, additions, suggestions.
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<P><PRE>$Id: reply-to-harmful.html,v 1.20 2002/11/15 03:46:04 chip Exp $</PRE>
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</PRE>
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