[ih] Fwd: Design choices in SMTP

[John Day]

> 
> I am fuzzy on all this but was this always the case?
> 
> As John points out, mail was originally part of FTP and mailboxes were files not directories. If one had multiple pieces of mail to deliver to the same mailbox would they have been done individually or all at once?  If so, when did delivering mail one at a time start? In SMTP? When mailboxes became directories?
> 
> (I would also note that Multics was uneasy giving an anonymous user Write access to a file so created Append access for use by mail.)
> 
>> On Feb 7, 2023, at 12:26, John Klensin via Internet-history <internet-history at elists.isoc.org> wrote:
>> 
>> Ralph,
>> 
>> I was not involved with the original SMTP design and don't remember ever
>> explicitly discussing those choices, but my guess is that the answer would
>> involve at least some of the following:
>> 
>> * SMTP was designed along the model of FTP, which preceded it as the mail
>> transport mechanism, and that made the command-response model seem natural
>> 
>> * At the time SMTP was designed, the network backbone and most
>> communications paths to it were running at 56 Kpbs, agonizingly slow by
>> today's standards.  Computers were much slower too.  Especially because all
>> of those round trips were within a single TCP session, that might have
>> contributed to exactly your suggestion that the intent was to get an SMTP
>> session that was doomed to fail over as soon as possible, in particular
>> before the payload was transmitted.
>> 
>> * Possibly more significant in retrospect than at the time, but a
>> command-response model like  "did I reach the right server?", "are you
>> willing to accept mail from this address?", "is this destination ok?", "how
>> about that destination?"  has some privacy advantages over a "here is the
>> envelope and payload, please do the right thing" model, even if the latter
>> is supplemented by a footer that has become common in some places. one that
>> essentially says "if this message was not really intended for you, please
>> un-read and delete it" .
>> 
>> You didn't ask but I hope your discussion noted that, for situations in
>> which minimizing round trips is considered important, the "pipelining"
>> option was introduced in 1995 (RFC 1854, succeeded by RFC 2920).
>> 
>>   john
>> 
>> 
>> On Tue, Feb 7, 2023 at 11:00 AM Ralph Holz via Internet-history <
>> internet-history at elists.isoc.org> wrote:
>> 
>>> Hi everyone,
>>> 
>>> During a lecture today, the following question came up: SMTP requires quite
>>> a few round-trips to deliver an email. Why was this design choice made,
>>> i.e., why does a submitting client not just send everything to the server
>>> in one RTT?
>>> 
>>> Apart from the client-server philosophy at play, I am wondering if that was
>>> because we wanted a receiver to terminate the delivery process as early as
>>> possible, i.e., before sending the body, if anything was amiss.
>>> 
>>> Does anyone have insights on that or maybe even know a nice write-up? I
>>> checked a few sites that discuss the history of SMTP, but so far no luck
>>> with this aspect.
>>> 
>>> Many thanks,
>>> Ralph
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>