[ietf-dkim] z= question with X headers

Should we add some text like “signers MAY exclude X type headers when 
calculating the z= tag?”  I was polishing our implementation today and 
integrating it and turned on the z= tag wherein my test messages promptly grew 
really large due to thousands of X headers (from SpamAssassin and other sources 
too).
 
Arvel

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