## /etc/exim4/conf.d/acl/40-check_data
  acl_check_data:
      deny message = Your mail is scored $spam_score spam points.\n\
                     Contact postmaster @ mouarf.org for further information.
           log_message = Pan ! $spam_score spam points. \n$spam_report
           spam = nobody:true
           condition = ${if >{$spam_score_int}{80}{1}{0}}

Voila, en esperant ne pas avoir de faux positif.