On Wed, 15 Dec 2004 11:11:38 -0800, Douglas Otis wrote:
Although the MAILFROM is set by the Submitter, it represents the
return-path.
Not really. It represents the bounce address.
There is no requirement that it have anything at all with reaching any of the
folks involved in creating or sending the message. In fact, there are
legitimate scenarios that set it to an entirely different address, in order to
separate bounce processing.
Current use of MAILFROM allows retaining this field to
avoid establishing a mailbox to handle returns. The HELO is closely
tied to host and thus is not as flexible as the Sender header, which is
also set by the Submitter.
HELO is quite flexible. It is set per session. In fact, it can be re-set
during a connection, to establish a new session.
What is distinctive about HELO is that it identifies an operator of the MTA
rather than anything about particular messages.
This seems to point to the Sender header as
being a good choice to reference Submitter signatures. There is an
exception allowed, in that when the From is the same as Sender, Sender
may be omitted. Perhaps a better way of viewing this would be to
consider the only valid field for Submitter signatures is the Sender
header, where this may be found, by virtue of compression, within the
>From header when it is not present within the message.
That is not an "exception". As you note, itt is merely an encoding efficiency
hack.
Folks need to understand that the logical rfc2822.sender value is ALWAYS
required.
d/
--
Dave Crocker
Brandenburg InternetWorking
+1.408.246.8253
dcrocker a t ...
www.brandenburg.com