Why some say "rpm hell"

[AP]

On Sun, Nov 24, 2013 at 6:50 PM, Tim <ignored_mailbox at yahoo.com.au> wrote:

> It doesn't require gmail to get messages threaded.  Threading is done by
> the message headers, each message has its own message ID, each reply has
> another header saying which message ID it's in reply to, and there's
> another header listing all the message IDs that belong in the same
> thread.

> The last one (in-reply-to) is used by mail clients to group all messages
> in a thread together.  The middle one (references) is used to thread
> them all together in the right order.

> Any mail client can do this.  Any mail client can break this, and some
> do, by not not adding in-reply-to headers, and not adding and
> maintaining the references header.  When they do that, they bugger it up
> for everyone else, as the data has been lost.

> Message threading is NOT done by whatever text is written in the subject
> line.  Though some broken clients think so.  Some helpful clients will
> try to use it, as well as threading headers, to fit in orphaned messages
> into a thread (broken by other crappy clients), or to break apart a new
> thread out of the middle of an existing one (when the subject line
> changed).  The latter not being a particularly good idea, either.

> To see messages in their properly threaded order, one needs to use a
> mail client that isn't broken in that regard (Evolution, Thunderbird,
> and many others work), and pick the option that threads messages in the
> message list window.

> Conversely, one can unpick that option, and sort messages via some other
> criteria - such as by "date," making a mess of the order of messages
> (hint - the generational order of which message came first, is done by
> what's a reply to what, not the date that it was read or written, dates
> are coincidental, not relational).

Thanks for taking time to explain this, I am re-reading to fully grasp it.