[erlang-questions] : Erlang Book - again

Adrian Ho <>
Thu Sep 7 20:57:50 CEST 2006

On Thu, Sep 07, 2006 at 02:41:34PM +0300, Dmitrii Dimandt wrote:
> (quoting the "Reply-To Munging Considered Useful" document): 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.

There's another kind of "damage" that the document doesn't describe, but
this one does:


Mail loops aren't theoretical: A list I was subscribed to some years
back (I forget which) had Reply-To-List set up, and everyone was happy.
Then one day, someone went on vacation and turned on his/her b0rken
autoresponder.  Within an hour, everyone on the list had almost a
thousand autoresponses in their inboxes.

Another list had:

* a mode that sent out list digests with Reply-To-List (which makes
  quite a lot of sense, on the surface), and

* a digest subscriber with a seriously b0rken autoresponder, that not
  only did not limit its response rate, but also quoted the entire
  incoming message right back

Within an hour, everyone[*] on the list had almost 200MB of list
"mail" that consisted solely of digests of digests of...ad infinitum.
Factor in the usual list archiving, and I think you can see where this
is headed.  The cleanup was, shall we say, painstaking -- and some folks
probably deleted mail they shouldn't have in the process.  The list
admin, naturally, was not amused and promptly "kicked" the offender.

[*] I lied: The lucky ones (like me) who had effectively unlimited mail
space got the 200MB.  The *unlucky* ones went over quota within minutes,
and may have lost other incoming email because of the mail loop.

Upshot: Reply-To-List works well 99.99% of the time, no argument there.
The 0.01% of the time it facilitates a mail loop, *everyone* suffers,
especially the list admin and his/her mail server.

Note of interest: SourceForge (the origin of the above URL) used to
*ban* Reply-To-List outright on all its lists because of the potential
for disaster that I described above.  It seems to have modified its
stance since then, probably because truly b0rken autoresponders are
quite rare nowadays.  It just takes one, though...

- Adrian

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