fold_headers 0 eliminates extra blanks which SpamAssassin would
otherwise add to 'fold' header-info over multiple lines
report_header 0 this moves the SpamAssassin report to the body of the
email, in case a message is suspected to be spam.
rewrite_subject 1 this enables subject-line modification
subject_tag {spam?} - with rewrite_subject enabled, if a message is
suspected to be spam, SpamAssassin will add this text to the subject of the
email
defang_mime 1
if a message is supected to be spam, SpamAssassin will also change html
to text, to prevent the email from 'calling home'
