From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dave Eckhardt <davide+p9@cs.cmu.edu>
To: 9fans@9fans.net
In-Reply-To: <9B525D75-6CBB-4E95-BE4F-83FCC7F1393B@ar.aichi-u.ac.jp>
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Content-ID: <26109.1219597103.1@lunacy.ugrad.cs.cmu.edu>
Date: Sun, 24 Aug 2008 12:58:23 -0400
Message-ID: <26110.1219597103@lunacy.ugrad.cs.cmu.edu>
Subject: Re: [9fans] dns failure in smtp
Topicbox-Message-UUID: 0683adfa-ead4-11e9-9d60-3106f5b1d025

> I think mx record is required in official dns server,
> although I feel  the condition is too strict.

Keep in mind that a DNS *failure* is not the same thing
as a particular DNS record not existing.

If you ask whether there is an MX record for foo, and
get a timeout, you can't assume there is not an MX
record for foo and "fall back" on the A query.

Misconfigured DNS servers with some frequency will
return SERVFAIL ("I am misconfigured or broken") to
an MX query while happily answering A queries.

The right thing is to request the administrator of
that domain to return an MX record to the MX query
or to return zero records.

Dave Eckhardt