27 May
2015
27 May
'15
8:27 p.m.
On 5/27/15 8:15 PM, Don Fanning wrote:
Here is a case where RFC's conflict.
They don't, re-read it.
RFC5321 in Section 5
[http://tools.ietf.org/html/rfc5321#section-5] states:
"The lookup first attempts to locate an MX record associated with the name. If
a CNAME record is found, the
resulting name is processed as if it were the initial name.*"*
This means if the lookup for www.example.com. returns CNAME example.com, it
will use the MX records under example.com., not anything under the CNAME
record www.example.com.
To add to the fun, a couple lines further into the
paragraph states that:
" If an empty list of MXs is returned, the address is treated as if
it was associated with an implicit MX
RR, with a preference of 0, pointing to that host."
So technically, every A record must be treated as a capable mail
exchanger even if there are no MX records.
No. Only if there is no other MX record returned will it use the A record as
a default. This is a last ditch effort, and there is nothing saying that a A
record identified host needs to run a mail exchanger on it.
--
Bryan Fields
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