[Users] Message-ID

[RW]

On Thu, 31 Jan 2013 19:23:51 -0500
Rich Pieri wrote:

> On Thu, 31 Jan 2013 22:15:43 +0000
> RW <rwmaillists at googlemail.com> wrote:
> 
> > It depends on where the rewrite occurs, there isn't any reference
> > header in the first mail in a thread. Aside from threading by
> > subject the only standard way to connect that to rest of the thread
> > is by its Message-ID.
> 
> There is no standards compliant way to maintain thread coherency with
> Internet mail. RFC 822 does not require anything usable be parsed from
> In-Reply-To and References. RFC 2822 requires that both headers have
> Message-ID strings in them. However, since it is perfectly valid for a
> single message to have multiple different Message-ID fields (a single
> reply to multiple messages, for example) you still cannot rely on
> Message-ID to be a reliable threading mechanism. It's nice when it
> works out but this is not required by mail handling standards. The
> only thing that can be depended on according to RFC 2822 is that every
> Message-ID generated by a mail system is unique.

That's all very well, but what relevance does it have to my statement
that the References headers don't eliminate the need for  Message-IDs?

  
> This is quite different from Usenet (RFC 1036) which requires
> Message-ID and References fields maintain thread coherency.


How is that consistent with your statement that "Message-IDs are not
necessary for threading"? How do you identify the first message in a
thread without looking at its Message-ID header?