On Mon, 7 Jan 2008, Jeroen Massar wrote:
'a' & 'b' are both separate MX's. As such according to the above pseudo-code,
which I deduced from the RFC, whenever 'a' is contactable and you can get a
response from it, you should honor that response. Thus if you contact 'a' and
it replies with a "450 Out of diskspace, try later" or other temp failure or a
5xx error etc, one should go to 'b'.
Postfix contacts a-AAAA, gets a 450 diskspace, then contacts a-A, gets the
same error again, and then tries b-AAAA and then b-A, which might accept the
message.
Exim does the same as Postfix. (I haven't checked what Sendmail does.)
When we last had this argument on the SMTP list the conclusion was that
the specification is not clear enough to decide what is correct, so it's
best to implement the most operationally practical algorithm. It depends
whether you think multiple address records for a name are only for
multi-homed hosts, or whether it's legitimate to point a single name at
multiple separate hosts.
Of course because some postmasters will think that their idea of "correct"
is the only possible one and try to implement an anti-spam policy on this
basis, disagreements inevitably lead to interoperability problems.
Tony.
--
f.a.n.finch <dot(_at_)dotat(_dot_)at> http://dotat.at/
FAIR ISLE: VARIABLE 4, BECOMING SOUTHERLY 5 TO 7, PERHAPS GALE 8 LATER. ROUGH.
SHOWERS. MODERATE OR GOOD.
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