Go to wordpress’s web directory and simply:

chown -R user:group * 
find . -type d -exec chmod 755 {} \;
find . -type f -exec chmod 644 {} \;

Edit the Postfix’s main.cf file and add the following line (or uncomment it):

header_checks = regexp:/etc/postfix/header_checks

Create /etc/postfix/header_checks file and add the following line:

/^subject:/ WARN

Finally, reload/restart Postfix. From now on there will be a “warrning: header subject” in your maillog.