John C Klensin wrote:
(1) My recommendation would be to retain the timeout, but note
that server implementations should be aware that some clients
will ignore the spec for operational reasons and apply a much
smaller number. My guess is that a discussion of the
appropriateness of doing that doesn't belong in an erratum/
corrigendum to 5321 but in a separate document (if at all).
I note, again fwiw, that I've been trying to get various
advocates for a ban (or near-ban) on NDNs to write that separate
document and propose a specific model at regular intervals since
well before 2821 was completed.
(2) How would people feel about moving toward changing the
"substantive text" to read something like:
"To avoid receiving duplicate messages as the result of
timeouts, a receiver-SMTP MUST carefully balance the
time required to respond to the final <CRLF>.<CRLF> end
of data indicator against the desirable goal of
rejecting undeliverable or unacceptable messages at SMTP
time rather than generating NDN messages later. "
I'll have to check whether "NDN messages" is the right reference
at that point, but it seems to me from the discussion that the
above should be about the right intent. We could go even a
little further and recast the paragraph as something like:
"Long delays after the <CRLF>.<CRLF> is received can
result in timeouts and duplicate messages. Deferring
detailed message analysis until after the SMTP
connection has closed can result in non-delivery
notifications, possibly sent to incorrect addresses. A
receiver-SMTP MUST carefully balance these two
considerations, i.e., the time required to respond to
the final <CRLF>.<CRLF> end of data indicator and the
desirable goal of rejecting undeliverable or
unacceptable messages at SMTP time."
I like the original clear and concise wording best (last paragraph of
section 6.1). All three say essentially the same thing about what the
receiver MUST do. The issue of avoiding NDNs is controversial, and
should be worked out in a separate document, as you suggest.
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