Date: Wed, 4 Oct 1995 10:56:17 -0700 (PDT)
From: Mark Crispin <MRC@CAC.Washington.EDU>
Sender: Mark Crispin <mrc@Tomobiki-Cho.CAC.Washington.EDU>
Subject: Re: What's the Sender header for? 
To: Keith Moore <moore@cs.utk.edu>
Cc: drums@cs.utk.edu
In-Reply-To: <199510040310.XAA26720@wilma.cs.utk.edu>
Message-Id: <MailManager.812829377.29737.mrc@Tomobiki-Cho.CAC.Washington.EDU>
Mime-Version: 1.0
Content-Type: TEXT/PLAIN; CHARSET=US-ASCII

On Tue, 03 Oct 1995 23:10:06 -0400, Keith Moore wrote:
> > >Furthermore,  RFC822 specifically  says (4.4.4)  that the  Sender: field
> > >should  be sent  notices of  non-delivery, etc.
> > Actually, I'd  like to put in  a motion that we  deprecate this. Nowadays
> > there seems to be a pretty clear agreement that in a SMTP environment you
> > MUST use MAIL FROM:<>, and  that in a non-SMTP environment "Return-Path:"
> > is your best bet.
> I second the motion.  Actually, I think this is pretty clear from RFC 1123,
> so we just need to clean up the text in the revised 822.

Agreed.  Unlike the other proposed deprecations, this one seems to be a
definite no-brainer.  It's there for historical reasons; this use of Sender is
from pre-SMTP days when there was no Return-Path.  Given current Sender usage,
this is an overload of the function of Sender.

The concern is what about environments which don't have a Return-Path in the
SMTP sense.  This seems to be a non-issue, since you can always generate the
header.

It may, however, be reasonable to specify defaulting, e.g.:
 Errors go to:
	Return-Path (MAIL FROM: information in SMTP environments) if known
	else Sender if known
	else From
  If an value is known, but empty, errors are to be discarded, and NOT sent to
  a value further down the list.

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