Re: [exim] Consider local_domains only if DNS matches

On 2007-05-16 at 23:42 +0200, Peter Thomassen wrote:
> Phil Pennock wrote:
> > A DNS RR for "*.example.org" will only supply data for those labels
> > which don't already have RRs; if you have an A record for
> > sub.example.org then "*.example.org MX 10 foo.example.org." won't
> > generate an MX response for "sub".
> >
> > Yes, anything which is a mail domain in a supported email address should
> > have MX records. If you're relying on A record fallback, you need "self
> > = pass".
>
> Uhm. I actually want to have a standards compliant DNS setup, but setting a
> an MX record for each subdomain (I don't know them in advance ...) looks a
> bit time-consuming. I hoped it was possible to specify wildcards for both
> the A and the MX types. But the day will come when I'll separate mail from
> web, and then I've got to fix all that afterwards since I cannot just
> change the A record of my MX host. Isn't there another smart way to come
> around that?

Okay, *if* the A record is faked up through a '*' response, then it
doesn't block the effect of the wildcard MX.

For a much better idea of the real world status of wildcard MX records,
the problems encountered and what should and shouldn't happen, try
reading RFC 4592, "The Role of Wildcards in the Domain Name System",
a standards-track clarification/update from July 2006.

That document includes examples, diagrams and so on, all to clarify when
records are faked up (sorry, "synthesized") and when they're not.

-Phil