On Thu, 20 Nov 2003, Willie Viljoen wrote:
> Infact, you could have an MX for a non-existant host, though stupid, it is
> legal:
>
> $ORIGIN example.com.
> foo IN MX 10 mail
> mail IN A 10.5.2.69
Why is this stupid? In your example, foo is a mail domain, and mail is a
host. What is the problem? This is exactly the way many, many mail
domains (including, to pick a local example from round here, cam.ac.uk)
are set up. Virtual mail domains and "corporate" mail domains are
typically of this type.
The only requirement for an MX record is that it points to a host name
and that name has one or more address records (either A or AAAA
records). The MX name does not have to be related to the host name, and
the host name can be in an entirely different DNS zone. If there is an A
record for the same name, it does not have to be the host to which the
MX points.
x.y.z. MX 10 a.b.c.
a.b.c. A 10.9.8.7
x.y.z. A 192.168.45.35
is perfectly legal, and 192.168.45.35 is not required to accept email.
--
Philip Hazel University of Cambridge Computing Service,
ph10@??? Cambridge, England. Phone: +44 1223 334714.
Get the Exim 4 book: http://www.uit.co.uk/exim-book
