[Evolution] Expression: (match-all (header-exists "X-Junkmail"))

[Luke Scharf <lscharf corepower com>]

I'm trying to remove anything that's been marked as spam out of my
long-term message archive.  But, I'd like to keep it so that I can train
bogofilter and stuff like that.  All of my mail is retrieved via POP and
is stored in local folders.

Anyway, I've tried to create a vfolder of just Spam.  My mail server
marks all suspected spam with the header "X-Junkmail:".  Since Evolution
doesn't provide the capability to search for an arbitrary header, and
since I've used Scheme before, I decided to try my hand at the
"expression box".

Some googling suggested that the following statement should do what I
want: 
        (match-all (header-exists "X-Junkmail"))
However, it returns precisely zero messages.

Other similar expressions (like "(match-all #t)") returns the number of
messages that I would expect (around 40,000).

Any suggestions?

Thanks,
-Luke