This is an example of some Postfix Header Checks which I use to help with mail spammers. This has been working as expected really well. One thing to note is that I did need to comment out #/^Precedence:.*bulk/ REJECT We do not accept your spam because it would prevent auto-reply emails from being sent such as vacation or out-of-office responses.

To load these header checks I am using the pcre format defined inside main.cf.

header_checks = pcre:/etc/postfix/header_checks