From: "Alan DeKok" <aland(_at_)freeradius(_dot_)org>
The idea is that the other end *already* walks down the list of MX's
by priority, if there's a delivery error.
What standards compliant SMTP client does that?
<shrug> So list them all as equal priority. RFC 974 says:
"All MXs at with a given value must be tried before any of a higher
value are tried"
You're missing the point. Any sort of filtering failure must be
treated as a permanent error by standards compliant SMTP clients. A
standards compliant SMTP client will never try another MX server of
any value for a given message after it has received a 5yz from the
first or any MX server that answered at all.
A standards compliant SMTP server will not immediately retry with any
other MX server after a 4yz from any MX server, but will instead try
again with the same (see page 42 of RFC 2821) or some other lowest
value MX server. RFC 2821 seems to be intentionally vague about how
long an SMTP client should wait before retrying, but typical sendmail
"queue runs" are separated by 5 to 30 minutes.
Minor details in the implementation of the idea don't prevent it
from working.
well....
Vernon Schryver vjs(_at_)rhyolite(_dot_)com
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