From: Robert Elz <Postmaster@munnari.oz.au>
To: Eric Thomas <ERIC@SEARN.SUNET.SE>
Cc: drums@cs.utk.edu
Subject: Re: What's the Sender header for? 
In-Reply-To: Your message of "Tue, 10 Oct 1995 17:43:59 +0100."
             <199510101654.MAA21216@CS.UTK.EDU> 
Date: Wed, 11 Oct 1995 03:24:33 +1000
Message-Id: <24183.813345873@munnari.OZ.AU>
Sender: kre@munnari.oz.au


    [...] there are two basic alternatives:
    
    1. The "Sender:" field was added  for no particular purpose.

This certainly happens, and it is probably not worth worrying
about.

    2. The "Sender:" field  was added for a good reason.

This also happens, and you certainly have the right to send replies
back there if you want to, regardless of it being quite clear
(as much as anything is) from the specs that that isn't the
intended use of the field.   A Sender who wants replies to go
to the Sender address, as well as the From address, really should
be inserting a Reply-To to cause that to happen.

But you left out the third case, which is the cause of most
Sender headers, including the one that should be in this message.

that is

3. the protocol specs say the header should be added.

The heeader really doesn't have a good reason to be there, but
there is a particular purpose.

I send mail from numerous different From: addresses, and my mailer,
obeying rfc822, dutifully installs a Sender header whenever I
provide the From: I wish to use for some particular message.

I most certainly do not want replies sent to my base address
if I am doing that.  If, as in this message, I am sending from
postmaster, then this must be postmaster related mail, and replies
should return to postmaster in the normal case.

You are certainly able to choose to send your reply anywhere you
like, including president@whitehouse.gov if it suits you, however
I doubt it is possible to rationally argue that setting things up
to reply to both From and Sender by default is a defensible
position.

kre