Pavel Kankovsky wrote:
> > 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?
>
> How does the way the 1st MX fails to accept the message affect the working
> of other MXes (in a general case)?
I think this is a good question.
Some believe that if the 1st MX is failing, that the mail to the 2nd or 3rd
MX will not reach the destination any sooner. I believe this is due to a
mistaken belief that the 1st MX is the same as the ultimate destination host
when in fact it may not be.
> > 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?"
>
> This is irrelevant. Qmail has no problem with this particular product of
> ignorancy unless it can somehow connect to the internal host and get
> disconnected (or get a temporary error during the conversation).
Even if the split DNS setup were done, the situation is still problematic for
Qmail if it won't backoff to the 2nd MX. If the ultimate destination is
behind a correctly configured firewall (you can't get there directly at all)
and the DNS has no MX record pointing direct, but both the 1st and 2nd MX
hosts can get there (special tunnel), then in the case of a failure of the
1st MX host, the 2nd MX host would mean a successful delivery ... missed by
Qmail if it doesn't want to try it.
--
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