smtp - mx domain is not making it into received headers

for example, the mx leech.bitmask.net shows up this way in the received headers:

Received: from mx1.riseup.net (mx1.riseup.net [198.252.153.129])
	by leech.localdomain (Postfix) with ESMTPS id A5B221F53B
	for ; Tue, 17 Sep 2013 18:40:01 +0000 (UTC)

*(from redmine: created on 2013-09-17, closed on 2013-10-03, blocks #3619)*