Mail threading behaviour is peculiar

On Feb 23, 2008, at 4:00 PM, George Wade wrote:

> Especially when a group name in the subject line is long: the way
> threading is organised has a touch of Artificial Insanity to it.
>
> It may be that a single language dictionary is being used while posts
> are international ? Though that is not sufficient for all the
> artificially split threads or strangely concatenated threads from
> quite different subjects. Another possibility is the large number of
> medical words in the Subject line. The threading engine may not
> recognise many of them ?

Mail.app (in common with other proper mail programs) uses the Subject:
header only as a last resort, when the expected message headers are
absent, when threading messages.

Testing indicates--as expected in a well-behaved program--that mail
uses a header like
In-reply-to: <60D5AD15-82DD-4BB9-9784-AFC61F6C209Dmac.com>
where the value inside the <> pair is the value of the Message-Id: in
the original message of the thread.

Eudora also seems to create In-reply-to:. It also seems to create
References: with the same value. "Seems to" because I don't know what
else the messages I looked at have passed through.

Unfortunately, Web Crossing seems to remove these known headers--
fairly large sample but enough to justify "seems to" but not "does".
Web Crossing also seems to provide its own header: X-webxref

So: Mail will behave quite sensibly in many situations--not so well
for this list.

Also, every so often one sees the injunction "Please don't hijack
threads" in mailing lists. Thread hijacking is taking a message that
came in, changing the subject, and sending out what that user believes
is the start of a new thread. It isn't, and so such messages and
replies thereto do indeed seem to jump back into the thread from which
they were hijacked.

Mailing list software has varying degrees of trouble dealing with
replies introduced by anything other than the RFC-required (suggested)
Re: Many non-English mail program do that. That can upset the
fallback subject-based threading.

Last paragraph from the mail help item found searching for
    message threads

Mail uses special headers in each message to determine if a message
belongs to a thread. If these headers are not present, the subject is
used to determine if a message belongs to the thread.

Threading should in theory not rely much on subject lines. If you look at the full headers of an e-mail message, there are at least 2 ways of indicating that the message is a response to a message with 'message-id' of XXXX .

The threading internals will look at these headers.

If you don't want something to be part of a thread then don't reply but start with a new e-mail message and cut/paste addresses or auto-fill or use contacts.
.

Jon



Jonathan Cohn

Thank you Jon and John,

The kind of list that I'm referring to would not take kindly to being
lectured about how to manage their threading behaviour: they have
too many real life urgencies to attend to. Well, I could put it into
a master file on efficient use of the lists concerned.

Funny, I've never seen this secret side of the Mail program discussed
before; now I can be more civilized in my replies. Next time I get
to the end of a reply -- realising that the subject and thread need
changing: it will be a quick new mail window and drag the body into
that. It never was deliberate perversity...

George

On 2008-02-25, at 14:17, Cohn, Jonathan C [IT] wrote:

> If you don't want something to be part of a thread then don't reply
> but start with a new e-mail message and cut/paste addresses or auto-
> fill or use contacts.

...or in Mail the pop-up menus over the address fields have an item
for New Message (to that address).

Hijacking comes up regularly on the FileMaker mailing lists I'm on, as
people will reply & change the subject instead of starting a new
message. The new thread then gets lost in the old one.