RE: [cobalt-users] MX record question / Raq4i

[SM <nntp@xxxxxxxxx>]

Hi,
At 11:53 18-12-2001 -0500, Chris Demain wrote:
><snip DNS trivia>
>
>I'm curious why, if all three MX to domain.com, why it can't be done thus:
>
>@ IN SOA ns1.example.com [and other soa foo]
>
>example.com.
>	IN	A	10.0.0.1
>	IN	NS	ns1
>	IN	NS	ns2
>	IN	MX	10	mail
>
>www	IN	CNAME	example.com.
>mail	IN	A	10.0.0.2

This can be done.

>It seems to me that accepting mail for user@xxxxxxxxxxxxxxxx is an issue for
>SMTP server configuration, and not the responsibility of DNS, and that DNS
>only becomes responsible when the MX for www != the MX for the domain.  It
>is also my understanding that in absence of an MX, mail to *.example.com is
>delivered to example.com's A record (i.e. I would think that it's much worse
>for a domain A RR to be missing than it is for a domain MX RR to be
>missing).

The issue is not whether the above configuration will work.  It is about
whether the configuration adheres to the RFCs.  You use a SMTP server to
run a mail service.  DNS has its responsibility in the configuration of a
mail server.  The RFCs state that a service accepting mail should have
valid MX record for all hosts which it serves.  They also states that the
domain name should have a valid MX record.  ALthough the remote system will
fall back to the domain A RR if there is no MX, that doesn't mean that
running a mail service for the said domain without a MX record is correct.

SMTP servers that adhere to the RFCs to the letter may reject mail from
servers which do not comply with the RFCs.

Regards,
-sm