debathena-msmtp constructs useless From lines for non-null instances

[jdreed]

If I run sendmail -t (or, more specifically, if I run a script that in turn runs sendmail -t), and a From: line is not specified, and I'm not using null instance tickets, I get mail that looks like this:

Received: from localhost (INFINITE-LOOP.MIT.EDU [18.152.1.6])
	(authenticated bits=0)
        (User authenticated as jdreed/root@ATHENA.MIT.EDU)
	by outgoing.mit.edu (8.13.6/8.12.4) with ESMTP id p1L24wU6009311
	for <jdreed@mit.edu>; Sun, 20 Feb 2011 21:04:58 -0500 (EST)
Date: Sun, 20 Feb 2011 21:04:58 -0500 (EST)
From: jdreed/root@MIT.EDU
Message-Id: <201102210204.p1L24wU6009311@outgoing.mit.edu>
To: jdreed@mit.edu

While the address is not invalid, it's entirely useless.

[jdreed]

r25065

[jdreed]

I've heard no feedback on this, and have built it. I'll note that if you're sending with a keytab _and_ omit the From line, this will result in mail from "host@…" or "daemon@…", but:
a) that's not obviously wrong,
b) those addresses reserved in moira,
c) don't do that,
d) there's no better option. Checking if the result is a user in hesiod will fail for, e.g. daemon, which has a passwd entry. I documented the failure in sendmail.8

[geofft]

WFM.

[jdreed]

Deployed 6/29