Building email threads from unix mailboxes

[Jed Parsons]

What headers to I have to know about to build thread trees from Unix
mailboxes?

Is it enough to get the In-Reply-To header for each message and build a
dictionary of { Message-ID: message } pairs?  Or is it more complicated
than that?

If there isn't already a module to do this (and apologies if there is
one and I don't know about it), are the current tools of choice the
'email' and 'mailbox' modules?  (And I guess I'd want to use the mime
decoding tools in 'email' to deal with messages that come with
attachments or html or other stuff.)

Thanks for any tips,

Jed