Subjects, Topics and Threading

[Lyndon Nerenberg]

> How is sending a new email any different than replying / changing subject 
> line?

A brand-new (not reply) message does not carry the References: header 
chain from the previous thread.  For threading-aware MUAs, this makes sure 
the new conversation doesn't get buried in the old thread.  Or possibly 
even ignored, as some MUAs can kill/ignore portions of threads based on 
specific message-ids in the References header.

--lyndon