On Thu, 1 May 2003 07:26:18 -0600 (MDT)
Vernon Schryver <vjs(_at_)calcite(_dot_)rhyolite(_dot_)com> wrote:
Have you watched an SMTP client responsible for passing a modest (few
1000 subscribers) or larger mailing list, particularly on hardware and
networks more than 10 years old?
Yup, did that for years.
Mailing list subscribers have always tended to be clustered on SMTP
servers, even before big ISPs like AOL.
The current distribution of target MXs is a lot different than the
picture 10 years ago. For one, the total number of target MXes for the
same size list population is more than an order of magnitude higher
today.
What may be more interesting is that the distribution curve is now and
was then a pretty standard power curve.
Requiring separate transactions for each addressee would increase the
load on the system by 10 times.
Some research has been done on this space, in particular with an
attention to increasing delivery performance for mailing lists to
variously standard distributions of destination addresses. Chuq von
Rospach did the most recent survey here that I'm aware of -- you can
find the numbers etc in the mailman-developers list archives.
Loose summary as I recall them: The optimal number of RCPT TOs per
message for best performance outbound delivery is approximately 5, and
is most definitely below 10.
My own testing with my list's MX distribution (known to be highly
unusual as AOL+Hotmail+MSN+Yahoo form less than 3% of my subscriber base
rather than the normal ~30% of most lists) confirms that 5 is pretty
close to the sweet spot for me as well.
I suspect that is why sendmail at least as early as the mid-1980s was
willing to sort by next-hop and use a single SMTP transaction when
possible.
I wouldn't hold Sendmail's design or approach up as any sort of
performance model. It has only very recently come back to being even
close to par in delivery performance against Exim, QMail and Postfix,
and then thru only very large and invasive changes to the delivery
architecture.
Given a $2,000US commodity machine its just not that hard to sustain
2,500 outbound deliveries a minute these days.
--
J C Lawrence
---------(*) Satan, oscillate my metallic sonatas.
claw(_at_)kanga(_dot_)nu He lived as a devil, eh?
http://www.kanga.nu/~claw/ Evil is a name of a foeman, as I live.
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