On Wed, 2004-05-19 at 10:14, Greg Connor wrote:
I thought of another consideration in the reuse-vs-new-rr discussion...
that is "additional" or "helper" records. Usually when you do an MX query,
you get the answer in the ANSWER section (like example.com IN MX 0
mail1.example.com) and you get additional information in the ADDITIONAL
section (such as mail1.example.com IN A 12.34.5.6)
<snip>
Assuming a query based off of the helo/ehlo domain, a SRV query such as
_smtp._tcp.__caa.my-ehlo-mx-host may also return the addresses within
the Additional Data section. (The "__caa" label ensures the namespace
of SRV is not affected.) Add a convention of matching the SRV helo/ehlo
domains responses to those of the MX record targets, and that solves the
problem of scaling to the number of SMTP hosts while still allowing
inbound and outbound to be handled by different hosts. In other words,
a record tailored to provide all information in one request.
Such a scheme allows a method to resolve the base domain by
investigating the MX records and then SRV records. If the helo/ehlo
domain is recorded in the headers, this provides a hint where to look
first to resolve for the base domain.
-Doug