title: Should I sign X headers in DKIM?
body: <p>I'm using Postfix + OpenDKIM to send emails. Should I sign X headers (X-Confirm-Reading-To, X-Unsubscribe, X-Priority, etc) in DKIM?</p>
  
  <pre><code>DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple;
      d=mydomain.com; s=mail; t=1435840997;
      i=no-reply@mydomain.com;
      bh=5n7rgNH/UhgzXvjmn6zu+M1BL29tq5L9PEZ7SB3uQgI=;
      h=To:Subject:Message-Id:From:X-Confirm-Reading-To:
       Disposition-Notification-To:Return-Receipt-To:List-Unsubscribe:
       List-Id:Date:X-Unsubscribe:X-Priority;
      b=vxfGzczj3S4wm1QtlrPPisyi2FsbDPP+gSSEyx/VWd09xdqSiLwdsn5vJS3SF5KoB
       etbHaJvmfvpbklJLwDPM4g7rRKaRmYXE3X02+E/DzsHFEz3TNPhPfkhNslMefRLf3h
       uq+juAwccQkzjxvvF5W4pukSJr1+Rw7NviukpZT5RSusiKSmJjFLjQavKCFSFme/bR
       u2zTCMEN1JUE5cLXKJV6aFfTl16HRXYimTNvI2pLGJijxku8zKaxrgQevQJM4v3EDX
       vs+gtOhw9t3kJI6OJsmJJyifiBRadl0/D3WUpvqYKGGFyzFPb28zvsI+h/AAOmapbM
       4WeE3vdYLb2Hg==
  </code></pre>
  
  <p>Which headers should be signed in DKIM?</p>