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Date:      Mon, 20 May 2002 11:48:23 -0700
From:      "Crist J. Clark" <crist.clark@attbi.com>
To:        Damon Anton Permezel <dap@damon.com>
Cc:        Peter Pentchev <roam@ringlet.net>, freebsd-qa@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG
Subject:   Re: 4.6-* sendmail misfeatures
Message-ID:  <20020520114823.D1468@blossom.cjclark.org>
In-Reply-To: <20020520122558.F962@damon.com>; from dap@damon.com on Mon, May 20, 2002 at 12:25:58PM -0500
References:  <20020520105154.E962@damon.com> <20020520191546.D349@straylight.oblivion.bg> <20020520122558.F962@damon.com>

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On Mon, May 20, 2002 at 12:25:58PM -0500, Damon Anton Permezel wrote:
> It is not a matter of a timeout.

Correct. The NS is actually reporting a transient error in response to
AAAA queries.

> The "A ?" come back fine.
> `dig' and 'nslookup' both resolve the name -- there is no timeout.
> `ping' works, for example.
> 
> Because sendmail "correctly" (aka: anal-retentively) adheres to a
> protocol, it flags this as an error,

Not sure what's so anal-retentive. The NS tells sendmail(8) there is
an error and sendmail(8) believes it.

> and doesn't attempt to try the
> "A ?" query.  This means that the outgoing mail sits in the queue forever.
> 
> This is not a particularly useful default behavior.
> 
> I have no control over austinenergy.com's DNS.  It has nothing to do
> with my ISP.  I am my own ISP, which is why I spent some time looking
> into this failure, to determine if it was a problem on my end.  It is,
> because I installed a broken sendmail.
> 
> The success of the internet has often been attributed in part to the
> philosophy stated in RFC 791.  I quote:
> 
> 	"The implementation of a protocol must be robust.  Each
> 	 implementation must expect to interoperate with others created
> 	 by different individuals. ....
> 	 In general, an implementation must be conservative in its sending
> 	 behavior, and liberal in its receiving behavior."

Too bad the people who wrote these broken DNS servers didn't follow
the rule.

> Burying a "we are correct" manifesto in some README and enforcing
> a default "correct" behavior results in breaking email connectivity.
> 
> It would be better to, perhaps, default to working, which I would
> prefer over it being silently, secretly and smugly "correct".
> If there really is a need to convert the world, syslog warning
> entries might be a less unfriendly way to alert the unwashed masses
> of the egregious violations of "correctness".

The issue is that the server is reporting a _transient_ failure. That
is, it's telling us that if we wait and try again later, we might get
a correct response. How do we know if it is a permanently broken
server or one that really is having a transient problem that will be
fixed soon? See 5.2.3 of RFC 1034.

Funny thing is that austinenergy.com seems to have one NS that deals
with AAAA queries in an OK-way and one that doesn't.
-- 
Crist J. Clark                     |     cjclark@alum.mit.edu
                                   |     cjclark@jhu.edu
http://people.freebsd.org/~cjc/    |     cjc@freebsd.org

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