email - Using a CNAME to forward traffic from a naked domain

I have a domain, flyh2.com.

I use a CNAME to forward www.flyh2.com to flyh2.elasticbeanstalk.com where my web site is hosted. This is the only way Amazon allows custom domain names. A records aren't allowed.

I'd like people to simply type http://flyh2.com (without the www) and still have visitors see my web site.

Originally I used CNAME to forward both the naked and the www records to my web site, but it seemed to cause problems.

Incoming mail was being returned to sender:

Fwd: Returned mail: see transcript for details
... Deferred: Connection timed out with flyh2.elasticbeanstalk.com.
Message could not be delivered for 6 hours
Message will be deleted from queue

Seems that the CNAME on the naked domain was overriding the MX records.

Now I've changed the CNAME on the flyh2.com record to point to www.flyh2.com and in turn www.flyh2.com to CNAME to flyh2.elasticbeanstalk.com.

My MX records are set up correctly, but the CNAME on the naked domain seems to override them. Do I have to use an A record?

Answer

You cannot have a CNAME for the domain.

CNAMEs can only exist as single records and not combined with any other resource records. Since a domain always has a SOA and NS record, you cannot use a CNAME for the domain. This is specified in RFC 1034, section 3.6.2.

The reason that email specifically breaks is found in RFC 5321, section 5.1:

That domain name, when queried, MUST return at least one address

record (e.g., A or AAAA RR) that gives the IP address of the SMTP
server to which the message should be directed. Any other response,
specifically including a value that will return a CNAME record when
queried, lies outside the scope of this Standard. The prohibition
on labels in the data that resolve to CNAMEs is discussed in more
detail in RFC 2181, Section 10.3.

In other words - as long as your provider does not allowed A records, what you want cannot be done.