[Evolution] Expanding a digest with procmail and showing it as threaded

[Mike Stilson <mike velgarian sytes net>]

I'm fairly new to using evolution (I've been a mutt fan until now) and
have run into a little problem.  I subscribe to digest versions of
several lists.  When I expand them (via procmail.. here's the script
that expands them)

:0:
* ^Subject:.*inux-kernel-.*digest
|formail +1 -a "List-ID: lkml" -ds >> $DEFAULT

:0:
* ^Subject:.*XFree86.*
|formail +1 -a "List-ID: xfree" -ds >> $DEFAULT
  
:0:
* ^List-ID:.*mysql.*mysql.com
|formail +1 -a "List-ID: mysql" -ds >> $DEFAULT

$DEFAULT is /var/spool/mail/mike

I set up evolution to filter on the List-ID header, and put them in
their own folder (I couldn't figure out how to get evo to break up the
digest itself, if it can), and that works just fine.

The problem comes that it won't thread any of the messages.  It's not a
BIG problem with smaller digests, but with lkml for example, there's
200+ a day in there and other than just grouping by subject then date, I
can't get it to thread at all.  Some threads wind up with 70 messages
and it'd be much more convenient to collapse them.

If I point mutt at the local evo mbox for it, it threads them fine,
since there's no reference id's in the digests, I assume it's threading
by subject.  Is there a way to set evo to do that?

TIA
-me