Default is to still look in body, but if you want the module to only
look in the defined header, use Set($CommandByMailOnlyHeaders, 1);

(Based on commit 2b533dc27f6a074b96a39c66379fc150a3f51ede from pr/3.)

[Adjusted tabs — s/\t/    /g — and simplified the $only_headers
conditional. -trs]