At 2:33 PM -0800 3/10/04, Dave Crocker wrote:
Paul,
PHI> The mail-ng transport protocol should be designed to only know about
PHI> a single hop, from sender to recipient. The sender may have multiple
PHI> hops to a designated transport agent, and the receiving transport
PHI> agent may have multiple hops to a mailstore, but the transport
PHI> protocol should not make any accommodation for these additional hops
PHI> other than to allow them to add metadata to the transit stream. These
PHI> requirements are to make the protocol more sensible and to limit the
PHI> responsibility of operators to just what they control.
How is this different from the current SMTP model?
In the current SMTP model, I believe we have been restricted from
having SMTP options that "speak for" SMTP servers further in the
chain. For example, we were prevented from making a "NO UCE" banner
because there was no way for the server making that claim to know
what SMTP servers behind it would have as policy. Different but just
as complex logic was used in 8BITMIME.
I am proposing that we think of transport as just between two
transport agents. What the receiving agent does with the message is
not part of the protocol. Said another way, the transport protocol
should not have rules that tell receiving agents what kind of policy
decisions they need to transmit further down the line.
--Paul Hoffman, Director
--Internet Mail Consortium