To record the email subject in the Postfix logs, simply add the following line to your Postfix header checks file:
With this done, restart the Postfix service. On Centos that is with the following command:
service postfix restart
Or is it? If you haven’t enabled header checks yet you need to do so in your mani.cf file under the postfix configuration directory (usually /etc/postfix). To do it, add this line to the bottom of that file:
header_checks = regexp:/etc/postfix/Header_checks
Now you can create that file (/etc/postfix/Header_checks) and add the line in for recording the subject.
When you are done, restart the postfix service.