[ On Tue, April 14, 1998 at 09:48:20 (+0100), Christopher Purnell wrote: ]
> Subject: Re: [EXIM] DNS
>
> There seems to be more and more broken DNSs these days and most of
> them seem to be running NT.
Hah. Yes, you get what you pay for, and when you buy Microsoft you pay
a very high premium, and a whole lot of "hidden" costs (uncountable,
really), for junk. But I guess we're preaching to the choir here....
> If the target of a MX record must have an A record why look for a MX
> record if you can't find an A record?
Because the algorithm for searching for the target mail host starts the
other way around -- As I think has been discussed in other followups to
this thread you must look for an MX first, and then the A's for all the
MX targets, and only as a last resort *may* you look for the A for the
target domain.
> > Exim should probably bounce the message with a "host not found" error,
> > perhaps with some detail saying that the MX is broken. I suppose it
> > could also freeze the message and alert the postmaster so she an go and
> > bug the owner of the MX for a fix.
>
> No, the correct behaviour is to deliver to one of the other targets of
> the MX record.
No, strictly speaking if the DNS is broken then it is impossible to
determine what the correct course of action should be. The only *sane*
reaction is to bounce the message. The insane among us might try and
automatically notify the contact in the SOA for the target domain that
their DNS is broken too.
> This is really causing us problems and I really need some sort of fix
> for it. Especially since some idiot moved all our machines from
> Oxford, where we are, to London.
Do a "whois" and/or 'host -t SOA target.domain' and/or equivalent to
find the contact information for the errant zone and *telephone* them
and ask them politely to fix their DNS. If they don't/won't then
blackhole their networks into /dev/null and tell your users they don't
exist on the Internet and they'll have to find some other communications
medium to use to connect with users at that site! [ ;-) 0.5 ]
In the mean time you might do something to short-circuit mail routing
for their domain in such a way that the DNS is not involved. Personally
I'd probably download a copy of their DNS zone, if possible, and fix it
locally and make my local nameserver authoritative for them, then I'd
hang a big sign on it to remind me to remove this hack when they finally
fix their own copy.
--
Greg A. Woods
+1 416 443-1734 VE3TCP <gwoods@???> <robohack!woods>
Planix, Inc. <woods@???>; Secrets of the Weird <woods@???>
--
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