Pavel Kankovsky writes:
> On Fri, 17 Sep 1999, Russell Nelson wrote:
>
> > Because you claimed that it was speaking SMTP. Upon examination, it
> > isn't. Your MX records are false. Why should I send your server any
> > mail at all, since it may not be the right server at all?
>
> 1. The host is dead => it does not send any datagrams =>
> it does not speak SMTP.
> 2. The host is alive but no process listens on SMTP port => it refuses
> TCP connections => it does not speak SMTP.
> 3. The host is alive, some process listens on SMTP port but something
> gets screwed up when a connection is open, and the connection is closed
> immediately (e.g. qmail-smtpd binary is corrupted and dies immediately)
> => it does not say SMTP hello => it does not speak SMTP.
> Why does qmail fall back to other MXes in cases 1 and 2 but not in
> case 3? Why does it fall back at all? It should always ignore the
> other MXes because the records are always incorrect according to
> your reasoning!?
Because it's reasonable to expect that other MX records will work for
1+2, but not for 3. If the lowest priority MX record is screwed up,
why aren't the others as well?
Essentially what we're dancing around is the issue of deliberate
misconfiguration in an effort to save sysadmin time: "It's hard work to
set up split DNS. Why not just have a low numbered MX record for
internal hosts, and a higher numbered record for external hosts? It
works for sendmail, so it should work for everything, right?"
--
-russ nelson <[EMAIL PROTECTED]> http://russnelson.com
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