[Exim] Detecting case of headers in a system filter

There's a particular spamware product out there that has a specific
pattern of setting some headers all in caps (and I don't mean the contents
of the headers, but the header fields themselves, like From: etc). Does
anyone have any suggestions on how I could match on that?

Thanks,

Tabor

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Tabor J. Wells                                     twells@???
Fsck It!                 Just another victim of the ambient morality