On Fri, Jul 27, 2012 at 12:34:58PM +1000, Russell Coker wrote:
On Fri, 27 Jul 2012, Tony Langdon <vk3jed@gmail.com> wrote:
wondering). However, you can't point an MX record to a CNAME, only an A (and/or AAAA for IPv6 capable MXs).
http://doc.coker.com.au/papers/benchmarking-mail-relays-and-forwarders/
Unfortunately you can do that and it seems to work.
some resolvers support it but it's explicitly documented not just as "undefined behaviour" but as something that you shouldn't do, same as pointing an MX at dotted-quad IP address will work with some resolvers but is prohibited by the standard. relying on the non-standard behaviour of some resolvers is a bad idea. it breaks your domain for everyone who doesn't use that (or similarly forgiving) resolver. as well as RFCs 1123, 2181, and related RFCs there are numerous resources on the net documenting this. Here's the first few hits from google: http://en.wikipedia.org/wiki/CNAME_record#Restrictions http://exchangepedia.com/blog/2006/12/should-mx-record-point-to-cname-record... http://serverfault.com/questions/81402/can-you-reference-a-cname-record-in-a...
It probably fails in corner cases and causes extra DNS work which is a bad thing.
it's more correct to say "it might work in some corner cases but don't do it". craig -- craig sanders <cas@taz.net.au>