Уточню, Received headers тут не "полученные заголовки", а конретный тип заголовка - Received. На ровне с "From:", "To:"... "Received:".

Примерно так они выглядят

Received: by 10.229.74.68 with SMTP id t4cs140410qcj;
Mon, 1 Nov 2010 09:09:25 -0700 (PDT)
Received: by 10.204.115.197 with SMTP id j5mr4507427bkq.205.1288627764250;
Mon, 01 Nov 2010 09:09:24 -0700 (PDT)
Return-Path: <lj_notify@livejournal.com>
Received: ...