title: postfix content filter per domain
body: <p>i testing postfix for my email server.
  i have to content filter all emails.</p>
  
  <p><code>master.cf</code></p>
  
  <pre><code>smtp       inet  n       -       n       -       -       smtpd -o content_filter=dfilt:
  ................
  dfilt     unix  -       n       n       -       -       pipe
     flags=Rq user=vmail:vmail argv=/opt/test/control.sh  -f ${sender} ${recipient}
  </code></pre>
  
  <p>when user sent to recipients on same domains,control.sh is one run
  but  user sent to recipients different domains control.sh is run per domain.
  so control.sh many runs for same email. i dont this because unnecessary work</p>
  
  <p>we can control.sh is only one run one email , not all recipients domain.
  i hope right explain my problem :-)</p>