Re: draft-ietf-imapext-thread

[Mark Crispin <[e-mail]>]

The problem is that threads are not like other types of data.  A message that
was not previously in a thread could join the thread as the result of the
addition of another message.  Put another way, a message's "thread status"
depends upon other messages.

Consequently, "thread status" is not at all per-message metadata.  It is
mailbox metadata.  If you subset the messages considered by the THREAD
command, the resulting tree is metadata for that subset, and not for any other
set (including a superset of that subset).

There isn't any known algorithm to update thread metadata with new messages,
either on a global or a per-message basis.  The only known way is to
recalculate the entire thread tree; and if the client needs to know it, to
transmit the entire tree to the client.