From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <5822959c74cc60ab78dec36a37e18d30@quintile.net>
From: "Steve Simon" <steve@quintile.net>
Date: Tue,  3 Jan 2006 12:13:58 +0000
To: 9fans@cse.psu.edu
Subject: Re: [9fans] smtp dns failure: mx lookup
In-Reply-To: <9bef2a2dfb71042935f1e86c22f57f1c@tombob.com>
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> echo smtp.comcast.net |ndb/dnsquery >/dev/null

Yep, this is what I do too, I followed it through smtp(8)
a while ago and came to the conclussion it was a 
caching problem in dns(8).

looking at /sys/src/cmd/upas/smtp/mxdial.c:163 

smtp looks up "smtp.comcast.net mx" but receives "dns failure"
and gives up.

dns should reply "resource does not exist" which would prompt
smtp to retry with "smtp.comcast.net ip" which will succeed.

If you force the "smtp.comcast.net ip" into dns's cache using
the manual query above then it replies "resource does not exist"
correctly and smtp completes as it should.

After some time the entry ages out of the cache and the
problem reappears.

I used ndb/dnsdebug to prove that it was not a dns config problem
and put it on my To-Do list, where it has gathered dust.

A little more info, but no fix - only the same old bodge, sorry

-Steve