If I add an MX record for a subdomain email address, do I also need to add a CNAME for that subdomain?

For example I want email addresses like *@mysubdomain.mydomain.com to be handled by a different server than *@mydomain.com so I add the following record:

MX mysubdomain handled by mail.anothermailserver.com with priority 10

Do I also have to add a CNAME as follows?

CNAME hr is an alias of 12.34.567.890

While I have the following A records:

A * points to 12.34.567.890
A mydomain.com points to 12.34.567.890
A mail points to 12.34.567.890

No. As long as mail.anothermailserver.com can be found, you are solid.

  • mail.anothermailserver.com does have to be an A record, it can't be a CNAME, but otherwise correct. – Chris S Jan 25 '12 at 2:14

I don't think you understand what a CNAME record is. A CNAME points an alias back to a canonical name. Your example of "hr" is what's called an A record.

If your concern is how will clients lookup the name "mail.anothermailserver.com", the answer is through mail.anothermailserver.com authoritative name servers.

To figure this out for yourself, try dig (or nslookup, host, equivalent for your OS) as follows:

dig mail.anothermailserver.com
  • The canonical name is the alias. It's the "standard" name, which points to a host name. – Chris S Jan 25 '12 at 2:17
  • … which only serves to make dmourati's point. The data portion of a CNAME resource record is not an IP address as in the question. – JdeBP Jan 25 '12 at 12:34

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