--On Wednesday, November 02, 2011 09:24 -0700 Douglas Otis
(3) Would such an extension be useful enough in practice, and
implemented and deployed enough in practice, to be worth the
trouble? I don't know and don't have an opinion.
And, to be explicit about it, I will listen intermittently, but,
because I no longer have significant responsibility for either
implementations or large-scale mail operations, expect to
continue to not have an opinion.
A short term "come back 15 minutes later" does not address a
much greater concern. Within IPv4, categorization of dynamic
or abusive sources currently abates a fair amount of undesired
traffic prior to establishment of a connection. This
abatement has become necessary for preserving resources within
smaller networks. IPv6 will soon offer a prefix space about
400,000 times larger than IPv4 unicast space. The greater
size of IPv6 and an inability to crawl its rDNS thwarts
similar efforts at either collecting or publishing similar
While SMTP could attempt to include an authentication process
within SMTP exchanges, an existing structure based on tickets
offers an extremely efficient alternative able to facilitate
use of LSNs and offers better control than that found with
"come back in 15 minutes".
You have said this, with small variations, many times. You are
certainly correct to warn others that you see that particular
danger with the interaction between IPv6 and larger-scale mail
operations. I'll let others, and history, figure out whether
you are correct or not.
In the context of the present discussion, I haven't noticed
anyone suggesting linking traffic control options and responses
to authentication, so I don't really understand where that part
of your comment is relevant. If you are suggesting either
replacing SMTP with a different type of mail model or, as you
have suggested before, replacing the DATA command and
transmission of content with some sort of pointer to where the
recipient can pick the content up... Well, by all means turn
those ideas into a coherent and comprehensive proposal and see
if you can get traction for it. But I'm not sure they are
relevant to the current discussion.