Local mail exchange and remote website? FIXED

[Eric Shubert]

On 10/18/2010 10:36 AM, Sandeep Bains wrote:
> I'm still bit puzzled on this. I think that the domain has no MX records
> listed and it is working with A record only

That's possible. See
http://www.dyndns.com/support/kb/email_mail_exchangers_and_dns.html
particularly the "Do I need MX records for my domain?" part. It's good 
practice to always have an MX record though. As the page says, some 
servers won't receive email from domains that don't have one.

> Or if as per the email; MX was pointing to a CNAME and now it is
> pointing to A?

That's my understanding (which may be incorrect).

> If things were wrong (as per your old configuration), where were those
> emails going to (in case you haven't made any changes on the system,
> they should had been accepted)....

They were going nowhere, as the submission was failing. The error 
message was given back to the client that tried to submit the message.

> It will be interesting to see all the resource records for the domain.
> As per the RFC the resolution should take place the following way
>
>     Once an SMTP client lexically identifies a domain to which mail will
>     be delivered for processing (as described in sections 3.6 and 3.7), a
>     DNS lookup MUST be performed to resolve the domain name [22].  The
>     names are expected to be fully-qualified domain names (FQDNs):
>     mechanisms for inferring FQDNs from partial names or local aliases
>     are outside of this specification and, due to a history of problems,
>     are generally discouraged.  The lookup first attempts to locate an MX
>     record associated with the name.  If a CNAME record is found instead,
>     the resulting name is processed as if it were the initial name.  If
>     no MX records are found, but an A RR is found, the A RR is treated as
>     if it was associated with an implicit MX RR, with a preference of 0,
>     pointing to that host.  If one or more MX RRs are found for a given
>     name, SMTP systems MUST NOT utilize any A RRs associated with that
>     name unless they are located using the MX RRs; the"implicit MX"  rule
>     above applies only if there are no MX records present.  If MX records
>     are present, but none of them are usable, this situation MUST be
>     reported as an error.

This is a little confusing all right. Which RFC is this from?
I believe that the SMTP client that's being referred to here is NOT the 
submitting client, but the relay host. TTBOMK submitting clients to not 
look up MX records as described here.

-- 
-Eric 'shubes'