The body of a mail message consists of everything following the first blank line to the end of the file. When you sent your sendstuff file, it contained only a body. Now edit the file sendstuff and add a small header.
Send this file to yourself again, running sendmail by hand as you did before:
Notice that our
From you@Here.US.EDU Fri Dec 13 08:11:44 1996 Return-Path: you@Here.US.EDU Received: (from you@localhost) by Here.US.EDU (8.8.4/8.8.4) id AA04599 for you; Fri, 31 Dec 96 08:11:44 -0700 Date: Fri, 13 Dec 96 08:11:43 From: you@Here.US.EDU (Your Full Name) Message-Id: <9631121611.AA02124@Here.US.EDU>