[dns-operations] Can MX be working with CNAME?

Jo Rhett jrhett at netconsonance.com
Mon Oct 21 14:14:51 UTC 2013

On Oct 21, 2013, at 4:37 AM, Tony Finch <dot at dotat.at> wrote:
> MX pointing to CNAME probably will work.

Not in my experience. Not with either sendmail or postfix.

> CNAME pointing to anything should work, except for the historical screwup
> in the way mail software handles CNAME.

Again, I don't perceive this to be a screwup. A CNAME to a domain is not a domain, it is a pointer to the canonical name. Thus, rewriting to the real domain is good behavior. Treating a CNAME as anything other than what it was intended to be is the screwup.

> Note that this does not just
> affect CNAME pointing to MX, but also CNAME pointing to A and CNAME
> pointing to AAAA, when the CNAME is used as a mail domain.

Tony, you seem to be confused about how dns and mail work. Fallback to host deliver when an MX doesn't exist was poor behavior in the original RFC, and has been fully deprecated behavior for more than 20 years now.  And yes, if you use a canonical name pointer at the far side of an @ sign, it should be rewritten to the domain it is pointing at. That is exactly that DNS and straightforward English indicates.

Jo Rhett
Net Consonance : net philanthropy to improve open source and internet projects.

Author of Instant Puppet 3 Starter: http://www.netconsonance.com/instant-puppet-3-starter-book/

More information about the dns-operations mailing list