Thanks to Renato Martins

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  HOW TO use MBL on Postfix:
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  a) edit file main.cf including the following lines:

# File with content filter for e-mail body
body_checks = regexp:/usr/local/etc/postfix/body-deny

  b) create a shell script to update body-deny like this:

#!/bin/sh
/usr/local/bin/wget -O - http://www.malware.com.br/cgi/submit?action=list_postfix > /usr/local/etc/postfix/body-deny
/usr/local/sbin/postfix reload 

  c) add this shell script to your cron for regular updates