[CentOS] Split dns issues

Mon Aug 3 14:39:47 UTC 2009
Filipe Brandenburger <filbranden at gmail.com>

Hi,

On Mon, Aug 3, 2009 at 10:27, Jason Pyeron<jpyeron at pdinc.us> wrote:
> My worry is the A record for the outsourced mail service is out of our control,
> if it were to change it would be catastrophic.

Well, if you *must* use a name like mx.google.com for your MX, you
could also set up an mx.google.com domain as authoritative in your
domain, and then add an "A" record with your internal mail server
there... It's not beautiful, but it should work.

Another alternative is to use "includes" in BIND, that way you could
have "views" for your pdinc.us zone, then on both of them you would
only have the MX record (which would be different on each of them) and
maybe the SOA record (but you could also decide to keep that on the
included file) and then an include to a file that contains the bulk of
the records for the zone. Would that solve your problem managing views
for that zone?

> I like the idea about the cname. Can a cname be used as a host for a MX record?

Not according to the RFCs, but in practice it does work. Beware that
you might stop receiving e-mails from very old and very buggy e-mail
servers though (like maybe Exchange 5 or very old Lotus Notes, but I
don't think anyone still uses those.)

> The other fear is the outsourced (showing ignorance on SMTP here) might react
> badly to the client making a connection to a server with a name different than
> they expected, as it looks like they are doing a name based virtual hosting.

I don't think so, since SMTP only uses the name of the MX server for
the TCP connection to the server's IP, nothing in the protocol later
will use that name again. Virtual hosting is usually done by having
the server accept e-mails to any of those e-mail domains on the same
server.

HTH,
Filipe