On Mon, 27 Sep 1999, Russell Nelson wrote:
> David Dyer-Bennet writes:
> > It doesn't work fine in the scenario I outlined at the beginning of my
> > message. In that situation, the mail will sit on the qmail system
> > until it expires, when there's a perfectly good secondary MX system
> > sitting there waiting to accept it. This is not my definition of
> > "works fine".
>
> Right, but you're suggesting that nobody will notice the lack of
> reception of email for seven days. If they make configuration changes
> without testing them (and I count leaving a down machine down as
> such), and then don't notice that something is broken for a week, then
> I'll wager that they'll be suited just as well without email.
Exactly. There seems to be some very odd ideas of what a higher-numbered
MX will do floating around in this discussion.
> You're also presuming that they have the ability to read email off the
> "secondary" host. It would be very unusual for a host which functions
> identically to another to be given a lower priority. Much more often,
> the secondary host is one which is configured only to relay mail to
> the primary.
Which is the defined behavior, and the default behavior in sendmail,
qmail, and most other mailers I know of.
Once the mail gets to the lowest-numbered MX, then any funny "local"
processing happens. If a host is configured as "fallback" but only for
use when the primary has a problem, yet the DNS is not changed to reflect
the seondary's new status when the primary does fail, then one is sending
the world mixed signals, and one gets what one deserves. The more typical
setup is to give them idenitical MXs, in which case even qmail will try
more than one given bad delivery problems.
> > The secondary MX exists to cover cases when the primary is down. It's
> > not an "incorrectly configured" DNS to have a primary MX listed that
> > happens to be down at the moment!
The secondary MX exists to receive mail for holding and requeuing to pass
onto the primary when the primary is not reachable by the sender and the
sender wants to unqueue the mail. If you're talking about failover, you
either need equal MX weights, or you need to have the DNS adjust when the
lower MX goes down. Anything else is a kludge, and an insistence thatthe
world support various kludges, when doing it right is quite simple.
As Russ noted, it may be not "incorrectly configured" DNS if the main mail
server is down, but it's certainly not correct if you have two hosts
acting as final mail destinations yet with differing MX weights, and you
expect there never to be a glitch if the lower-numbered one is acting
sort-of alive yet is unable to really receive mail.
-M
Michael Brian Scher (MS683/MS3213) Anthropologist, Attorney, Policy Analyst
Mainlining Internet Connectivity for Fun and Profit
[EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED]
Give me a compiler and a box to run it, and I can move the mail.
