This is exactly the problem with the current model. SMTP *is* an
end-to-end system.
Says who? SMTP explicitly allows for source routing in addresses. This is not
something tacked on as an afterthought -- it is a well documented and
heavily used aspect of the protocol. The host requirements RFCs have
confirmed the status of routing in SMTP.
The text you quote from the host requirements simply states that SMTP is
a host-to-host mail exchange protocol. In a store and forward environment,
how do you come to the conclusion that this means end-to-end?
Additionally, consider the common situation where two sites are served by
MX records, and communicate via another transport other than SMTP (UUCP for
example). When users in these environments communicate, they do so, and in
fact SMTP may be involved, but there is never a chance that either of the
end systems will ever communicate with each other using SMTP directly.
Even if you don't like UUCP type examples, there are plenty of examples
where sites that have IP connectivity in the Internet have several MX
records in place, in case there exists problems in directly connecting with
the end system. So, for these situations, it may be only be SMTP that is
involved, but *one hop at a time*, and not the originating system directly
communicating with the eventual end system.
I'm sorry, but I simply don't see any evidence, either in the RFC's nor in
the way the Internet works, that supports the notion that SMTP is an
end-to-end system. Now, if we are talking about addressing in the Internet,
this is a different issue...
Regards,
Tim Kehres