Re: draft-lilly-from-optional-01.txt

At 07:18 23-02-2005, Bruce Lilly wrote:
>Responding to your points in reverse order:
>
>The message header field "Sender" is an originator field which is
>not necessarily related to the SMTP envelope sender return path (or
>similar mechanisms in protocols other than SMTP).  Consequently, it
>plays no role in authentication.

I agree that the "Sender" field may not necessarily be related to the SMTP 
envelope sender.  The field may be used for end-to-end authentication 
technologies.  The From and/or Sender headers are the only fields available 
to the MUA for making any determination as to the reputation of the sending 
domain.

>The draft addresses two separate cases where the From field is
>inappropriate: 1) where the author has no Internet mailbox (this
>is not a case of anonymity) and 2) where the author requires
>anonymity.  In the first case, specifying a Sender field is certainly
>possible, though not particularly useful (details below).  In the
>second case, a Sender field may be harmful; it might directly
>or indirectly (when the guys with firearms show up demanding to
>know who a message's author is) defeat anonymity.  In the case of
>an individual author who requires some degree of anonymity, the
>claim that supplying that author's mailbox in a Sender field does not
>affect anonymity doesn't bear much scrutiny.

We rarely if ever see a genuine case one in practice.  Case two is 
interesting.  The guys will firearms will show up demanding who is the 
message's author even if you don't include a Sender as they will have the 
IP address of the relay.  My suggestion is to have the mailbox of the 
Sender in the Sender field.  That does not affect the anonymity of the 
message's author.

>The Sender field is not particularly useful; it is NEVER used
>automatically in responses (RFC 822 sect, 4.4.2, also RFC 3834) --
>the Reply-To field exists for support of the first case above where

I understand that the Sender field is never used in response.

>So while I would carefully consider such a requirement if there's
>a sound case for it, the "authentication" argument does not
>constitute such a case, since message originator fields are not
>intended for authentication protocol use.  Such consideration also
>needs to take into account both reasons for making the From field
>optional; putting information in a differently-named field does
>not take anonymity into account.

My point is not about server-side authentication.  Message originator 
fields can and may be used for authentication.  Quoting RFC 822 section 4.4.2:

   "This field contains the authenticated identity of the AGENT (person, 
system or
    process) that sends the message."

On a different note, you wrote "As such, it improves security for message 
authors who require anonymity." under security considerations.  People 
requiring anonymity are better served by using anonymous remailers instead 
of excluding the From field from their message.

Regards,
-sm