Broken list threads

[David Woodhouse]

On Sun, 2011-04-03 at 17:01 +0100, Andy Waddington (software devel)
wrote:
> Sometime before sending, David Woodhouse typed (and on Saturday 2011-04-02 sent):
> > On Sat, 2 Apr 2011, Jonathan Wiltshire wrote:
> > 
> > > Some mail clients, usually the ones written with lists in mind, have a
> > > shortcut to reply only to the list. In mutt it's Shift-L.
> > 
> > Although many people frown upon that feature and consider it extremely 
> > rude to drop people from the discussion by using it: 
> > http://david.woodhou.se/reply-to-list.html
> 
> Other people consider it very rude to reply direct to them as well as the
> list, so that they get the reply twice.

Yes. It's a choice between two evils. Which is worse?
 - To drop someone from the discussion entirely, when they have actively
   taken part in it already, or
 - To cause someone to receive two copies of an email.

Now consider the fact that it's trivial for people who *really* want to
avoid "duplicates" to filter them out on the receiving end, by dropping
the second message that arrives with the same Message-Id. Does that
change the choice at all?

>  What works for mailing lists which only allow posts from people
> subscribed to the list is not the same as those which allow anyone to
> post.

It changes the equation slightly. But don't forget that if a list bars
posts from non-subscribers, that just forces people who *occasionally*
want to contribute, or who read mail through the archives as Vangelis
does, to "subscribe" and either disable mail delivery, or just filter it
into a folder that they almost never look at.

So just because the list forces people to subscribe, that doesn't
*necessarily* mean that they'll see a message if you drop them from Cc
when you're replying to them.

> Also, typically, it breaks the system by which mailing list messages get
> filed in their own mailbox (because people filter on the "To:" field
> containing the mailing list name, and may not check "Cc:" and so on. This
> clogs personal mailboxes). 

That's just broken filtering; you should never filter on the recipients
in the To/Cc headers. They may bear *no* relationship to the actual
recipient of the messages, or the reason why *you* are receiving it.

> One thing that is a universally bad idea is to reply to the sender, and
> blind CC to the list, so that the list name doesn't get put anywhere that
> recipients can filter on it...

That's incorrect. Compare the two copies of this message that you
receive, for example. There are at least three things you could filter
on which are *unique* for the copy that arrives through the list.

In order of accuracy:

The *best* thing to filter on is the SMTP reverse-path, which may
appears in a Return-Path: header by the time the message is delivered.
It should match get_iplayer-bounces.*@lists.infradead.org.

Second best thing is a Sender: header, which will be
get_iplayer-bounces at lists.infradead.org.

Third (and less reliable than the above two) is a List-Id: header of
get_iplayer.lists.infradead.org. This one is less reliable because it
fails in the case which might seem obscure, but which does actually
happen to me:
 - You *are* (or have been) subscribed to the list.
 - You filter the list messages into a folder.
 - You have mostly lost interest, and never look in that folder.
 - Someone knows that you don't actively read the list, and sees a
   message on the list that they *know* you may be interested in.
 - This 'someone' sends the the message to you. Instead of forwarding
   it, they 'resend' (or bounce or redirect) it, so the original message
   is intact for you to reply to.

The List-Id: filter would catch that message and drop it into the list
folder even though it was sent *personally* to you. Filtering on
reverse-path or sender is the only 100% reliable option.

-- 
dwmw2