On Wed, May 27, 2015 at 5:27 PM, Bryan Fields Bryan@bryanfields.net wrote:
(Please trim inclusions from previous messages)
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.
That is not true at all. The previous paragraph states that it must process the entire FQDN and not many any inferences as to the domain's relationship with the FQDN.
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.
You are absolutely correct. You don't have to run a smtpd on it at all. It just states that where there is lack of a MX record that it should treat the FQDN of the mail as the MX with a preference of 0. If it doesn't connect then it goes through retry logic until it's dropped to the floor.