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<title>MetaSystema.Net: Reply-To Munging Considered Useful</title>
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<h1>This Page is a Mirror</h1>
<p>This page has been mirrored for historical preservation</p>
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<H2 ALIGN=CENTER>Reply-To Munging Considered Useful</H2>
<H3 ALIGN=CENTER>An Earnest Plea to Mailing List Administrators</H3>
<H4 ALIGN=CENTER>Last revised: 3 January 2000</H4>
<HR>
<P>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.
<P>While the message is being processed, the list administrator might
take advantage of the opportunity to
<A HREF="http://www.fwi.uva.nl/~mes/jargon/m/munge.html">munge</A> some
of the message headers. Many list administrators want to add a
<KBD>Reply-To</KBD> header that points back to the list. This transformation
is also one of the most useful.
<P>Some administrators claim that <KBD>Reply-To</KBD> munging
can have harmful -- even dangerous -- effects. I assert the opposite,
that <EM>not</EM> adding a <KBD>Reply-To</KBD> header has even more
harmful effects. If you think
<KBD>Reply-To</KBD> munging is a <EM>bad</EM> idea, I hope I can change your
mind.
<H3>RFC 822 and "Text Message Teleconferencing"</H3>
<P>The first thing to consider is that
<a href="http://www.faqs.org/rfcs/rfc822.html">RFC 822</a>, the document which
defines the standards and usages for email, specifically mentions this usage in
section 4.4.3:
<pre>
A somewhat different use may be of some help to "text message
teleconferencing" groups equipped with automatic distribution
services: include the address of that service in the "Reply-To"
field of all messages submitted to the teleconference; then
participants can "reply" to conference submissions to guarantee
the correct distribution of any submission of their own.
</pre>
<P>Aside from this official sanction, there are a number of reasons for munging
the <KBD>Reply-To</KBD> header. The arguments which follow are my own.
They may not be comprehensive, but I think they are compelling.
<H3>The Principle of Minimal Bandwidth</H3>
<P>The ``Principle of Minimal Bandwidth'' is a good rule that will keep
you out of trouble. It says that you <EM>should</EM> make any changes
which will reduce the amount of email traffic on the Internet.
The ``Principle of Minimal Bandwidth'' will help you avoid the sorts of
problems we are about to discuss. This principle <EM>is</EM> a rule
designed to be broken, but you can avoid some significant heartache
by thinking hard and long before you do so.
<H3>Reply-To Munging Adds Something</H3>
<P><KDB>Reply-To</KDB> gives the respondant an option which would not
otherwise exist: namely the ability to <EM>reply only to the list</EM>.
Despite the fact that many (though not all) email clients have the
ability to "reply to sender" or "reply to all recipients", many list
subscribers want to <EM>reply only to the list</EM>, which is not the
result of selecting either of these options. So, to ensure that the
reply goes to the list, they select "reply to all recipients", which
generally results in the sending of <EM>at least two</EM> email messages, one
to the list, and one to the original sender.
<P>This is frequently quite annoying to the original sender, who now
receives two copies of the reply. Furthermore, in many cases the original
sender has added additional recipients. Not only does "reply to all
recipients" send the reply to each of these additional recipients
(who are frequently also members of the list), it also propagates this
list of recipients onto the reply to the list.
<P>The effects of this snowball, as each additional person replies to the
messages using "reply to all recipients", they become the sender, and thus
get added to the list of recipients with the next reply. Thus the list of
recipients grows and grows. Frequently, as the subject matter changes,
members of the list find themselves receiving multiple copies of messages
which have strayed from the topic in which they were originally interested,
<i>even after they have unsubscribed from the list</i>.
<P>Many people have pointed out that it is relatively easy to implement a
<KBD>procmail</KBD> filter to remove duplicates. This attitude merely reveals
a Unix-centric and US-centric viewpoint. Many users of inferior operating
systems <i>do not</i> have a tool powerful enough to ensure the removal of
duplicate messages. Furthermore, in many European countries, connect time is
charged by the <i>minute</i>. Even with <KBD>procmail</KBD>, the duplicates
have to be <i>downloaded</i> before they can be filtered, resulting in
unnecessary additional expenses for some of our European list mates.
<P>This last fact reveals that the issue is really related to bandwidth.
By applying the ``Principle of Minimal Bandwidth'', we conclude that it
is necessary to add a <KBD>Reply-To</KBD> header that points back to the list.
<H3>It Doesn't Break Reasonable Mailers</H3>
<P>If you use a reasonable mailer, <KBD>Reply-To</KBD> munging <EM>does</EM>
provide new functionality, namely the ability to <EM>reply only to the
list</EM>. Furthermore, it does <EM>not decrease</EM> functionality. In Pine,
for example, when there is a <KBD>Reply-To</KBD> header, Pine will ask,
``Use "Reply-To:" address instead of "From:" address?'', easily allowing
one to reply only to the original author. In KMail, it is even easier. One
merely right-clicks on the hyperlinked <KBD>From</KBD> address.
<P>If your mailer doesn't have this option, you should request it from its
development team. Any mailer, whose development team refuses this simple
request due to some ideological position, cannot be said to be reasonable.
<H3>Freedom of Choice</H3>
<P>Since <KDB>Reply-To</KDB> munging adds additional functionality, it actually
<EM>increases</EM> freedom of choice. Not only can you now <EM>reply only to
the list</EM>, you still have the option to reply to the original
author, or to all recipients, easily and conveniently.
<H3>Some Mailers are Broken</H3>
<P>There are, unfortunately, some poorly implemented mail programs that lack
separate "reply-to-author" and "reply-to-group" functions. A user saddled
with such a mailer can benefit from <KBD>Reply-To</KBD> munging. It makes
it easier for him or her to send responses directly to the list.
<P>Furthermore, this change <EM>does not</EM> penalize the conscientious
person that uses a reasonable mailer. Reasonable mailers give one the
ability to reply to the <KBD>From</KBD> address. Therefore, it would be
unkind to further penalize those with poorly implemented mail programs, since
munging the <KBD>Reply-To</KBD> header causes no harm to those with reasonable
mailers.
<H3>Principle of Least Total Work</H3>
<P>For discussion type lists, I would estimate that ninety percent of the time,
people want to reply to the list. Without munging, they either have to break
the ``Principle of Least Bandwidth'', or type in the list address. Many people,
being lazy, will choose the former, sending unnecessary copies of emails to
people who will either have to delete them, or take the time to set up a
filter (if they are lucky enough to be running an operating system which
facilitates this).
<P>On the other hand, about ten percent of the time, replying to the sender
might be more appropriate. Even if the respondant has an unreasonable
mailer (a decision for which they are probably responsible), the worst case
scenario is that they have to type in an address ten percent of the time.
Of course, if they took the time to add this recipient to their address book,
they could reduce the amount of typing to a minimum.
<P>So, which produces least total work: typing in the list address ninety
percent of the time (plus possibly taking the time to set up a filter), or
typing in an individual's address ten percent of the time?
<P>I'll take munged <KBD>Reply-To</KBD> headers every time, thanks.
<H3>People are Responsible for Their Own Mistakes</H3>
<P>Some administrators claim that munging <KBD>Reply-To</KBD> headers is
harmful because it surprises people, and can cause damage when things go
awry. They assert that administrators should prevent the possibility of a
private message being mistakenly broadcast to the entire list.
<P>This is simply not the responsibility of the administrator. People are
responsible for their own mistakes. If someone is sending a private email
which is derogatory, or otherwise embarrassing were it to be made public,
they should probably be sending it directly, rather than as a reply to a
public message. They should also pause and think about whether they should
be sending it at all. This pause should be quite sufficient for a
conscientious person using a reasonable mailer to catch any mistake that
they might be about to make.
<P>In any case, it is an entirely trivial matter for the list administrator
to provide an obvious clue in the subject line of every message that the
message was received from a mailing list. If your Mailing List Manager doesn't
provide an option to prepend "[listname]" to the subject, then switch to one
that does (&nbsp;e.g. <a href="http://www.list.org/">GNU&nbsp;MailMan</a>
or <a href="http://www.greatcircle.com/majordomo/">Majordomo</a>&nbsp;).
<H3>And in the End...</H3>
<P>If you are not convinced yet, then allow me one final plea. Most mailing
lists are intended to facilitate discussion on a given topic. If this is
indeed the primary purpose of your list, then you <EM>really should</EM> add a
<KBD>Reply-To</KBD> header which directs replies to the list. This helps to
ensure that the entire thread of the conversation is available to all who
might be interested.
<P>I can't count the number of times I have searched the archives
of a list for a solution to a problem, only to find the question asked, but
no solution. Yet, when I subsequently post the question to the list, the
long-time members insist that it has already been discussed, and that I should
search the archives. If I'm lucky, a newer member forwards to me the private
reply which answered the question.
<P>Thus, munging the <KBD>Reply-To</KBD> header benefits those lists which are
intended for serious discussion. If your list is intended primarily for
announcements or other one-way mailings, you may safely ignore these arguments.
<H3>It's What People Want</H3>
<P>I have been and am subscribed to both munging and non-munging mailing lists.
On the non-munging lists, there are regular requests to change the list so
that <KBD>Reply-To</KBD> replies to the list. On the munging lists which
already do this, there are hardly any requests for change.
<H3>Summary</H3>
<P>Many people want to munge <KBD>Reply-To</KBD> headers. They believe
it makes reply-to-list easier, and it encourages more list traffic.
It really does both of these things, and is a very good idea. To reiterate:
<UL>
<LI>It adheres to the principle of minimal bandwidth.
<LI>It provides additional functionality to the user.
<LI>It increases a subscriber's freedom to choose how to direct a response.
<LI>It does not reduce functionality for the user of a reasonable mailer.
<LI>It aids and assists the user with a deficient mailer.
<LI>It adheres to the principle of least total work.
<LI>It helps to ensure that questions are answered on the list.
<LI>Your subscribers want you to do it.
</UL>
<P>&nbsp;
<H3>Addendum</H3>
<P>There are, of course, a few details that need to be addressed to make
<KBD>Reply-To</KBD> munging more pleasant and productive for everyone. One
potentially serious problem with <KBD>Reply-To</KBD> munging is the possibility
of mail loops. It should be possible for the list server to detect and prevent
this. If anyone has any patches to implement this feature, I would be happy
to provide a link to the patch on your ftp server, or to make it available on
my own ftp server.
<P>Also, patches are needed for any mailers that do not implement the ability
to reply to the <KBD>From</KBD> address. Please send links or patches to me
at <i>sdhill&nbsp;at&nbsp;metasystema.net</i>. Thanks.
<H3>Patches</H3>
<P>
A patch for Emacs rmail is available at: <a href="http://www.metasystema.net/pub/patches/emacs/rmail-query-reply-to.el">http://www.metasystema.net/pub/patches/emacs/rmail-query-reply-to.el</a>.
<H3>Dissenting Opinion</H3>
<P>I originally wrote this essay as a response to Chip Rosenthal's
<a href="harmful.html">
Reply-To Munging Considered Harmful</a>.
<p>
<address>Simon Hill</address>
<address>sdhill&nbsp;at&nbsp;metasystema.net</address>
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