--On Tuesday, 25 March, 2008 23:18 -0400 Keith Moore
<moore@xxxxxxxxxxxxxxxxxxxx> wrote:
>> You know, that's a very interesting point. One of more common
>> configuration variations we see is to disable MX lookups and
>> just use address records.
>
> how does anyone expect that to work across administrative
> domains?
Sorry, I'm now completely confused. Maybe it has just been a
long day, but...
Ned, by "disable MX lookups", do you mean "don't put MX records
into the DNS zone and therefore force a fallback to the address
records" or "ignore the requirement of the standard that
requires using MX records if they are there"? If the latter,
the behavior, however useful (or not) is, IMO, so far outside
the standard that it is irrelevant to any discussion about how
DNS records are used in a standard way.
Keith, what do administrative domains have to do with this? If
I can write
foo.example.com. IN MX 0 foo.example.com.
foo.example.com. IN A 10.0.0.6
then, as things are now specified, I can lose the MX record
entirely with no difference in effect. Similarly, if I can write
foo.example.net. IN MX 0 foo.example.com.
foo.example.com. IN A 10.0.0.6
Things still work as predicted if I discard the first record,
keep the second, but either know to reference the relevant SMTP
server as "foo.example.com" or, if I don't need
"foo.example.net" for anything else, insert a record in the
"example.net" zone that looks like
foo.example.net IN CNAME foo.example.com.
Certainly there are cases where that is administratively
burdensome, or at least annoying. There are also cases in which
I need multiple MX records, not a single implicit one. But, for
these fairly common cases...
john
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