Re: Submission and SMTP SRV records
2004-03-17 08:13:04
--On Tuesday, 16 March, 2004 18:19 -0600 "Eric A. Hall"
<ehall(_at_)ehsco(_dot_)com> wrote:
On 3/16/2004 6:09 PM, Keith Moore wrote:
which market is that?
The people that have an email address (100%), and for whom SRV
lookups would work 90% of the time.
Eric,
With respect, I don't believe this either. The reality is that
there are a number of cases for locating submission servers,
depending on network topology and technical restrictions. I
can't even guess at the percentages, but I'd guess that "90%" as
a description of the number of cases in which, not only would
SVR lookups "work", but that they would yield a good result and
solve enough of the problem to be worth the trouble would be
_very_ high.
I would characterize the approach of the proposal in
draft-hall-email-srv-00.txt as "find the name of the server that
matches your email address given organization preferences". As
we have discussed, that makes sense for some situations. But,
even within that model:
* Getting to that server may, in practice, require
either special authentication setups or running a tunnel
to get to the server, a tunnel that might otherwise not
be present. The presence or absence of SRV information
is not likely to be a big help with that so, for some
cases, Keith's argument (as I interpret it) that enough
hand-configuration is required that SRV doesn't solve
enough of the problem to be worth the trouble may be
very relevant.
* You wrote in a later note... "Moreover, SRV "works" in
more situations than all of the others. I mean, DHCP is
pretty cool but it doesn't "work" when I'm dialing up
from an airplane and getting "local" PPP (that changes
every 300 miles) and no localized proxy gateway to my
home server". Well, I don't think that, on that
airplane, the SRV model in the draft is going to work as
expected either, at least unless your organization has
an implementation of dynamic DNS that might be
considered to go past the basic model of the DNS spec
(giving you widely different answers based on the IP
address range from which your query came) and had a
fairly intimate relationship with the airline. That is
probably a case of the model outlined below, but need
not be (and it raises a whole collection of trust
issues).
More important, it isn't the only model. In today's network,
where ACL restrictions on SMTP connections outgoing from
particular subnets are common (I'm not suggesting that they are
a good idea, only that they are common), it would make far more
sense to support an inquiry for "submission server that I can
reach from my address and that will accept my relay traffic".
That could, of course, be done with an SRV setup and a different
style of query. Or it could, in principle and in many cases, be
done with DHCP when (or after) the local host or gateway address
is assigned (but no one I know of supports that either).
Keith has addressed some of the other cases here, and I won't
bother to repeat them.
That said, Keith, what convinced me to put my fingers into this
proposal wasn't a "this is good" argument, much less a "90%"
one. I'm still very skeptical about SRV use for anything
off-LAN, where I see it filling in for some of the deficiencies
that you identify with DHCP. But it is something that people
are obviously going to think about -- the fact that Eric and
Pete started doing so is evidence of that. I suggest that the
benefits of interoperability in cases of "if you are going to do
this [possibly dumb] thing, then doing it the same way that
others do" justifies some work and, if you will, standardization
_without_ a recommendation to implement. I hope the proposal
--which I hope you have read by now-- is clear that it is in
that "if you decide to do something like this..." category. If
it is not, I (and I hope Eric) would welcome text. I would even
welcome text along the lines outlined in some of your notes,
e.g., a clear statement of the cases for which this particular
approach is not applicable, the problems it doesn't solve even
within the applicable range, etc.
john
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- Re: Submission and SMTP SRV records, (continued)
- Re: Submission and SMTP SRV records, Keith Moore
- Re: Submission and SMTP SRV records, Eric A. Hall
- Re: Submission and SMTP SRV records, Keith Moore
- Re: Submission and SMTP SRV records, Eric A. Hall
- Re: Submission and SMTP SRV records, Keith Moore
- Re: Submission and SMTP SRV records, Eric A. Hall
- Re: Submission and SMTP SRV records, Keith Moore
- Re: Submission and SMTP SRV records, Keith Moore
- Re: Submission and SMTP SRV records, Eric A. Hall
- Re: Submission and SMTP SRV records, Keith Moore
- Re: Submission and SMTP SRV records,
John C Klensin <=
- Re: Submission and SMTP SRV records, Pete Resnick
- Re: Submission and SMTP SRV records, John C Klensin
- Re: Submission and SMTP SRV records, Lyndon Nerenberg
- Re: Submission and SMTP SRV records, Pete Resnick
- Re: Submission and SMTP SRV records, Lyndon Nerenberg
- Re: Submission and SMTP SRV records, Eric A. Hall
- Re: Submission and SMTP SRV records, Lyndon Nerenberg
- Re: Submission and SMTP SRV records, Eric A. Hall
- Re: Submission and SMTP SRV records, Arnt Gulbrandsen
- Re: Submission and SMTP SRV records, Keith Moore
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