Setting up a CNAME record for any of the domains or subdomains that you've got within a hosting account will enable you to direct it to a different domain/subdomain. The forwarded domain will lose all of its records - A, MX etc, and will take the records of the domain it's being pointed to. In this light, you simply can't set up a CNAME record to point your domain to a third-party company and maintain a functional e-mail service with the first hosting company. Also, it is important to note that a CNAME record is always a string of words and never a number as it's frequently wrongly identified as the A record of the domain name being forwarded. One of the primary uses of a CNAME record is to point a domain name that you own through one provider to the servers of some other company if you have set up a site with the latter. In this way, the site will appear under your own domain name, not under some subdomain provided by the third-party provider.